large excursions of action within the resonance of a degenerate hamiltonian system with two degrees of freedom we investigate the width of the resonance zone in a degenerate hamiltonian system with two degrees of freedom in which the hamiltonian lacks the quadratic term in the taylor expansion this leads to larger excursions of action in the phase space than the nondegenerate one and corresponding resonance frequency widths would become narrower however in contrast to the nonautonomous hamiltonian system with one and half degree of freedom we find that the above case is not generic and only occurs at particular resonances an example relevant to the interaction of resonances is considered analytic results are verified in numerical simulations

interference rejection in ffh systems using least squares estimation techniques a fast frequency hopped ffh receiver which uses a prewhitening filter to reject narrowband interference is described by using an appropriate fractional tap spacing it is shown that interference can be estimated independently of the desired signal bit error rate results are presented for the receiver for linear square law combining the results compare favorably to those obtained by a near optimal automatic gain control agc combining technique the performance of the prewhitening filter interference rejection method is shown to be superior to that of a nonparametric self normalizing receiver finally simulation results for an ffh receiver using the complex least mean square lms algorithm to update the prewhitening filter coefficients are presented

novel graphical representation of genome sequence and its applications in similarity analysis abstract in order to compare different genome sequences an alignment free method has been proposed considering the essential property of sequence is sequentiality we define a compound transformation which transforms a genome sequence into a sparse 16 by l 1 matrix m based on 16 kinds of 2 mer dinucleotides furthermore we found the transformation above mentioned is an order preserving transformation opt based on the theory of matrix analysis we derive a 16 dimensional vector to characterize a genome sequence via singular value decomposition svd of m finally we analyze the similarities among multiple sequences from 20 eutherian species the experiment results show that our approach performs well in the field of sequence analysis

nonmonotonic twist maps abstract we investigate a family of nonmonotonic radial twist maps constructed by unfolding the linear twist function we find several new modes of reconnection and derive conditions for them to occur reconnection and bifurcation of higher order resonances are studied in detail including vortex pairs and triplets the structural instability of some of these exotic figures is mitigated by the presence of chaotic separatrix layers invariant curves of involution pairs are utilized to locate and chart their often very complex metamorphoses

chaotic scattering theory of transport and reaction rate coefficients the chaotic scattering theory is here extended to obtain escape rate expressions for the transport coefficients appropriate for a simple classical fluid or for a chemically reacting system this theory allows various transport coefficients such as the coefficients of viscosity thermal conductivity etc to be expressed in terms of the positive lyapunov exponents and kolmogorov sinai entropy of a set of phase space trajectories that take place on an appropriate fractal repeller this work generalizes the previous results of gaspard and nicolis for the coefficient of diffusion of a particle moving in a fixed array of scatterers

the birth of twin poincare birkhoff chains near 1 3 resonance for a typical area preserving map we describe the birth process of two twin poincare birkhoff chains i e two rings consisting of center points alternated by saddles wound around an elliptic fixed point these twin chains are not born out of the elliptic fixed point but in the plane from an annular region where the rotation number has a rational extremum this situation generically occurs near a 1 3 resonance we find that the birth of two twin pb chains in such an annular region requires first the birth of two dimerized chains of saddle center pairs by a tangent bifurcation the transition from two dimerized chains to two pb chains involves the breakup of homoclinic saddle connections and the formation of heteroclinic connections it amounts to the reconnection phenomenon of howard and hohs our results can be regarded as a supplement to the poincare birkhoff theorem for the case that the twist condition is not satisfied

critical exponents for a transition from integrability to non integrability via localization of invariant tori in the hamiltonian system critical exponents that describe a transition from integrability to nonintegrability in a two dimensional nonlinear and area preserving map are obtained via localization of the first invariant spanning curve invariant tori in the phase space in a general class of systems the position of the first invariant tori is estimated by reducing the mapping of the system to the standard mapping where a transition takes place from local to global chaos the phase space of the mapping shows a large chaotic sea surrounding periodic islands and limited by a set of invariant tori whose position of the first of them depends on the control parameters the formalism leads us to obtain analytically critical exponents that describe the behaviour of the average variable action along the chaotic sea the result is compared to several models in the literature confirming the approach is of large interest the formalism used is general and the procedure can be extended to many other different systems

multiple emitter location and signal parameter estimation processing the signals received on an array of sensors for the location of the emitter is of great enough interest to have been treated under many special case assumptions the general problem considers sensors with arbitrary locations and arbitrary directional characteristics gain phase polarization in a noise interference environment of arbitrary covariance matrix this report is concerned first with the multiple emitter aspect of this problem and second with the generality of solution a description is given of the multiple signal classification music algorithm which provides asymptotically unbiased estimates of 1 number of incident wavefronts present 2 directions of arrival doa or emitter locations 3 strengths and cross correlations among the incident waveforms 4 noise interference strength examples and comparisons with methods based on maximum likelihood ml and maximum entropy me as well as conventional beamforming are included an example of its use as a multiple frequency estimator operating on time series is included

on slater s criterion for the breakup of invariant curves abstract we numerically explore slater s theorem in the context of dynamical systems to study the breakup of invariant curves slater s theorem states that an irrational translation over a circle returns to an arbitrary interval in at most three different recurrence times expressible by the continued fraction expansion of the related irrational number the hypothesis considered in this paper is that slater s theorem can be also verified in the dynamics of invariant curves hence we use slater s theorem to develop a qualitative and quantitative numerical approach to determine the breakup of invariant curves in the phase space of area preserving maps

a high resolution data adaptive time frequency representation a data adaptive time frequency representation is developed that overcomes some limitations of the short time fourier transform while avoiding the cross terms that make the wigner distribution and other bilinear representations difficult to interpret the adaptive time frequency representations uses gaussian basis functions but varies their time width and chirp rate with time and frequency to achieve high signal concentration everywhere a measure of local signal concentration allows fully automated determination of the optimal basis parameters the adaptive method is computationally expensive but may provide much better performance than any currently known technique

the defocusing mechanism of isochronous resonances abstract we present a numerical study concerning the defocusing mechanism of isochronous resonance island chains in the presence of two permanent robust tori the process is initialized and concluded through bifurcations of fixed points located on the robust tori our approach is based on a hamiltonian system derived from the resonant normal form choosing a convenient parameter in this system we are able to depict a comprehensive analysis of the dynamics of the problem

the vanishing twist in the restricted three body problem abstract this paper demonstrates the existence of twistless tori and the associated reconnection bifurcations and meandering curves in the planar circular restricted three body problem near the lagrangian equilibrium l 4 a twistless torus is created near the tripling bifurcation of the short period family decreasing the mass ratio leads to twistless bifurcations which are particularly prominent for rotation numbers 3 10 and 2 7 this scenario is studied by numerically integrating the regularised hamiltonian flow and finding rotation numbers of invariant curves in a two dimensional poincare map to corroborate the numerical results the birkhoff normal form at l 4 is calculated to eighth order truncating at this order gives an integrable system and the rotation numbers obtained from the birkhoff normal form agree well with the numerical results a global overview for the mass ratio 4 3 is presented by showing lines of constant energy and constant rotation number in action space

chaotic hamiltonian systems survival probability we consider the dynamical system described by the area preserving standard mapping it is known for this system that p t the normalized number of recurrences staying in some given domain of the phase space at time t so called survival probability has the power law asymptotics p t ensuremath sim t ensuremath ensuremath nu we present new semiphenomenological arguments which enable us to map the dynamical system near the chaos border onto the effective ultrametric diffusion on the boundary of a treelike space with hierarchically organized transition rates in the framework of our approach we have estimated the exponent ensuremath nu as ensuremath nu text ln text 2 text ln 1 r g ensuremath approx 1 44 where r g sqrt 5 ensuremath 1 2 is the critical rotation number

a novel graphical representation of proteins and its application abstract on the basis of three kinds of indices of physicochemical properties of twenty amino acids a novel 3d graphical representation of protein sequences is presented then the improved cumulative distance of the 3d graphical representations is defined in order to compare the proteins for similarity furthermore the efficiency of our approach is illustrated by performing a comparison of similarities dissimilarities among sequences of the nd5 proteins of nine different species a correlation and significance analysis is provided to compare our results on similarities dissimilarities and some other graphical representation results with the clustalw results on similarities dissimilarities the comparison results show that our approach has better correlations with clustalw for all nine species than other approaches

subspace analysis of spatial time frequency distribution matrices spatial time frequency distributions stfds have been previously introduced as the natural means to deal with source signals that are localizable in the time frequency domain previous work in the area has not provided the eigenanalysis of stfd matrices which is key to understanding their role in solving direction finding and blind source separation problems in multisensor array receivers the aim of this paper is to examine the eigenstructure of the stfd matrices we develop the analysis and statistical properties of the subspace estimates based on stfds for frequency modulated fm sources it is shown that improved estimates are achieved by constructing the subspaces from the time frequency signatures of the signal arrivals rather than from the data covariance matrices which are commonly used in conventional subspace estimation methods this improvement is evident in a low signal to noise ratio snr environment and in the cases of closely spaced sources the paper considers the music technique to demonstrate the advantages of stfds and uses it as grounds for comparison between time frequency and conventional subspace estimates

a blind source separation technique using second order statistics separation of sources consists of recovering a set of signals of which only instantaneous linear mixtures are observed in many situations no a priori information on the mixing matrix is available the linear mixture should be blindly processed this typically occurs in narrowband array processing applications when the array manifold is unknown or distorted this paper introduces a new source separation technique exploiting the time coherence of the source signals in contrast with other previously reported techniques the proposed approach relies only on stationary second order statistics that are based on a joint diagonalization of a set of covariance matrices asymptotic performance analysis of this method is carried out some numerical simulations are provided to illustrate the effectiveness of the proposed method

short time fourier transform using a bank of low pass filters the purpose of this paper is to present some experimental results estimating instantaneous frequencies of fm frequency modulation signals using the short time fourier transform stft method the relevant stft coefficients were computed using a bank of simple one pole low pass filters which estimates the cross correlation of a given signal and complex sinusoids also it is shown that computing the stft coefficients is equivalent to finding the least square solution which best approximates the given signal as a weighted sum of complex sinusoids

linear frequency modulated signal detection using radon ambiguity transform a novel time frequency technique for linear frequency modulated lfm signal detection is proposed the design of the proposed detectors is based on the radon transform of the modulus square or the envelope amplitude of the ambiguity function af of the signal a practical assumption is made that the chirp rate is the only parameter of interest since the af of lfm signals will pass through the origin of the ambiguity plane the line integral of the radon transform is performed over all lines passing through the origin of the ambiguity plane the proposed detectors yield maxima over chirp rates of the lfm signals this reduces the two dimensional 2 d problem of the conventional wigner ville distribution wvd based detection or the radon wigner transform rwt based detector to a one dimensional 1 d problem and consequently reduces the computation load and keeps the feature of built in filtering related issues such as the finite length effect the resolution and the effect of noise are studied the result is a tool for lfm detection as well as the time varying filtering and adaptive kernel design for multicomponent lfm signals

escape of particles in a time dependent potential well we investigate the escape of an ensemble of noninteracting particles inside an infinite potential box that contains a time dependent potential well the dynamics of each particle is described by a two dimensional nonlinear area preserving mapping for the variables energy and time leading to a mixed phase space the chaotic sea in the phase space surrounds periodic islands and is limited by a set of invariant spanning curves when a hole is introduced in the energy axis the histogram of frequency for the escape of particles which we observe to be scaling invariant grows rapidly until it reaches a maximum and then decreases toward zero at sufficiently long times a plot of the survival probability of a particle in the dynamics as function of time is observed to be exponential for short times reaching a crossover time and turning to a slower decay regime due to sticky regions observed in the phase space

bilinear signal synthesis in array processing multiple source signals impinging on an antenna array can be separated by time frequency synthesis techniques averaging of the time frequency distributions tfds of the data across the array permits the spatial signatures of sources to play a fundamental role in improving the synthesis performance array averaging introduces a weighting function in the time frequency domain that decreases the noise levels reduces the interactions of the source signals and mitigates the crossterms this is achieved independent of the temporal characteristics of the source signals and without causing any smearing of the signal terms the weighting function may take noninteger values which are determined by the communication channel the source positions and their angular separations unlike the recently devised blind source separation methods using spatial tfds the proposed method does not require whitening or retrieval of the source directional matrix the paper evaluates the proposed method in terms of performance and computations relative to the existing source separation techniques based on quadratic tfds

array processing for nonstationary interference suppression in ds ss communications using subspace projection techniques combined spatial and time frequency signatures of signal arrivals at a multisensor array are used for nonstationary interference suppression in direct sequence spread spectrum ds ss communications with random pn spreading code and deterministic nonstationary interferers the use of antenna arrays offers increased ds ss signal dimensionality relative to the interferers interference mitigation through a spatio temporal subspace projection technique leads to reduced ds ss signal distortion and improved performance over the case of a single antenna receiver the angular separation between the interference and desired signals is shown to play a fundamental role in trading off the contribution of the spatial and time frequency signatures to the interference mitigation process the expressions of the receiver signal to interference noise ratio sinr implementing subspace projections are derived and numerical results are provided

lv s distribution principle implementation properties and performance this paper proposes a novel representation known as lv s distribution lvd of linear frequency modulated lfm signals it has been well known that a monocomponent lfm signal can be uniquely determined by two important physical quantities centroid frequency and chirp rate cfcr the basic reason for expressing a lfm signal in the cfcr domain is that these two quantities may not be apparent in the time or time frequency tf domain the goal of the lvd is to naturally and accurately represent a mono or multicomponent lfm in the cfcr domain the proposed lvd is simple and only requires a two dimensional 2 d fourier transform of a parametric scaled symmetric instantaneous autocorrelation function it can be easily implemented by using the complex multiplications and fast fourier transforms fft based on the scaling principle the computational complexity properties detection performance and representation errors are analyzed for this new distribution comparisons with three other popular methods radon wigner transform rwt radon ambiguity transform rat and fractional fourier transform frft are performed with several numerical examples our distribution is demonstrated to be a cfcr representation that is computed without using any searching operation the main significance of the lvd is to convert a 1 d lfm into a 2 d single frequency signal one of the most important applications of the lvd is to generate a new tf representation called inverse lvd ilvd and a new ambiguity function called lv s ambiguity function lvaf both of which may break through the tradeoff between resolution and cross terms

local polynomial fourier transform receiver for nonstationary interference excision in dsss communications the problem treated in this paper is monocomponent nonstationary interference excision in direct sequence spread spectrum dsss communication systems by means of the local polynomial fourier transform lpft first the interference is optimally concentrated in the time frequency t f plane and then its t f signature is removed via a binary mask the lpft receiver is derived in matrix form and its optimization is performed having in mind an influence of the binary mask on the received signal the conventional suboptimal and the optimal lpft receiver performances are compared by means of simulations carried out on the received signal corrupted by different fm types of interferences the short time fourier transform stft receiver is considered as a special case of the lpft receiver and its performance is assessed simultaneously with the lpft receiver both in conventional and optimal case

3 d maps and coupling numbers for protein sequences abstract based on a five letter model of the 20 amino acids we propose a new 3 d graphical representation of protein sequence then we derive from the graphical representation numerical indices called 3 d coupling numbers to characterize protein sequences the examination of the similarities dissimilarities among the globin proteins of 15 species illustrates the utility of the approach

an investigation of chaotic diffusion in a family of hamiltonian mappings whose angles diverge in the limit of vanishingly action the chaotic diffusion for a family of hamiltonian mappings whose angles diverge in the limit of vanishingly action is investigated by using the solution of the diffusion equation the system is described by a two dimensional mapping for the variables action i and angle theta and controlled by two control parameters i epsilon controlling the nonlinearity of the system particularly a transition from integrable for epsilon 0 to non integrable for epsilon ne 0 and ii gamma denoting the power of the action in the equation defining the angle for epsilon ne 0 the phase space is mixed and chaos is present in the system leading to a finite diffusion in the action characterized by the solution of the diffusion equation the analytical solution is then compared to the numerical simulations showing a remarkable agreement between the two procedures

discrete time local polynomial approximation of the instantaneous frequency the local polynomial approximation lpa of the time varying phase is used to develop a new form of the fourier transform and the local polynomial periodogram lpp as an estimator of the instantaneous frequency if spl omega t of a harmonic complex valued signal the lpp is interpreted as a time frequency energy distribution over the t spl omega t spl omega sup 1 t spl omega sup m 1 t space where m is a degree of the lpa the variance and bias of the estimate are studied for the short and long time asymptotic behavior of the if estimates in particular it is shown that the optimal asymptotic mean squared errors of the estimates of spl omega sup k 1 t have orders o n sup 2k 1 and o n sup 2 m k 1 2m 3 k 1 2 m respectively for a polynomial spl omega t of the degree m 1 and arbitrary smooth spl omega t with a bounded mth derivative

a simple scheme for adapting time frequency representations we propose a simple efficient technique for continuously adapting time frequency and time scale representations over time the procedure computes a short time quality measure of the representation for a range of values of a free parameter and estimates the optimal parameter value maximizing the quality measure via interpolation

weak chaos and poincare recurrences for area preserving maps the spectrum f t of poincare recurrence times for the standard map exhibits two distinct limits an integrable weak coupling limit with an inverse power law and a chaotic strong coupling limit with exponential decay in the domain where chaotic regions coexist with integrable structures the spectrum f t exhibits a superposition of exponential and power law decay such a law can be proved to occur in a model of area preserving map at the boundary of the mixing and integrable components

analysis of dft based frequency excision algorithms for direct sequence spread spectrum communications the capacity of direct sequence spread spectrum modulation to reject narrow band interference can be significantly improved by eliminating narrow band energy at the receiver in a process called frequency excision this paper considers several algorithms that operate on the real time discrete fourier transform dft of the received signal to perform frequency excision the case in which only the signal and additive white gaussian noise awgn are present at the receiver is considered as a means of comparing the relative performance of different algorithms that operate without knowledge of the power spectral density of the interference an approach for analysis using the postcorrelation signal to noise ratio snr as the figure of merit is presented that is valid for a broad class of spreading modulations first the algorithm that sets a fixed fraction of the frequency domain record to zero is examined using rank order statistics as an analytical tool this result is then generalized to confirm previous estimates of snr degradation for the algorithm that sets all values that exceed a threshold to zero these results are again generalized to apply to the algorithm that sets a fixed fraction of the band to a fixed amplitude while retaining phase information in an algorithm called fraction clip the relative performances of several clip algorithm options are derived as special cases finally a performance measure of the algorithms in the presence of multiple narrow band interference is provided and illustrated with an example

resonant islands without separatrix chaos an alternative type of hamiltonian nonlinear resonant island is analyzed in the usual case where the resonant island is pendulumlike chains bifurcated out of the central elliptic point undergo infinite cascades of period doubling bifurcations as they approach the island boundary in the present case we find that those chains undergo either period doubling or inverse saddle node bifurcations depending on the strength of perturbing terms in the saddle node case we show that just after a reconnection process external chains cross the island boundary to collapse against the bifurcated internal chains

scaling invariance of the diffusion coefficient in a family of two dimensional hamiltonian mappings departamento de fisica unesp universidade estadual paulista avenida 24a 1515 13506 900 rio claro sao paulo

improving the readability of time frequency and time scale representations by the reassignment method in this paper the use of the reassignment method first applied by kodera gendrin and de villedary 1976 to the spectrogram is generalized to any bilinear time frequency or time scale distribution this method creates a modified version of a representation by moving its values away from where they are computed so as to produce a better localization of the signal components we first propose a new formulation of this method followed by a thorough theoretical study of its characteristics its practical use for a large variety of known time frequency and time scale distributions is then addressed finally some experimental results are reported to demonstrate the performance of this method

a quantitative snr analysis for the pseudo wigner ville distribution a quantitative analysis for short time fourier transform has been previously given we analyze the snr for the pseudo wigner ville distribution with rectangular windows for multicomponent signals in additive noise the snr for the pseudo wigner ville distribution in terms of a sampling rate is given for a fixed window length

linearly constrained direct sequence spread spectrum interference rejection a constrained least squares technique is presented that utilizes a modified optimality criterion which enhances the detection capabilities of direct sequence spread spectrum systems the standard least squares rejection filter adds distortion to the decision variable at the output of the despreading operation constraints are introduced into the least squares solution of the rejection filter which reduce the self noise of the filter while simultaneously retaining its interference rejection properties two types of constraint conditions are considered the first is a correlation matching property for the rejection filter output this constraint induces the filter to pass the chip sequence undistorted the second type of constraint is energy reduction which induces the filter to achieve minimal energy both constraint types are successful at increasing the output signal to noise ratio snr simulation results are presented which demonstrate the output snr improvement by using the constrained rejection filter

adaptive time varying cancellation of wideband interferences in spread spectrum communications based on time frequency distributions the paper proposes an adaptive method for suppressing wideband interferences in spread spectrum ss communications the proposed method is based on the time frequency representation of the received signal from which the parameters of an adaptive time varying interference excision filter are estimated the approach is based on the generalized wigner hough transform as an effective way to estimate the instantaneous frequency of parametric signals embedded in noise the performance of the proposed approach is evaluated in the presence of linear and sinusoidal fm interferences plus white gaussian noise in terms of the snr improvement factor and bit error rate ber

scaling properties for a family of discontinuous mappings abstract scaling exponents that describe a transition from integrability to non integrability in a family of two dimensional nonlinear and discontinuous mappings are obtained the mapping considered is parameterized by the exponent in the action variable the scaling exponents describing the behavior of the average square action along the chaotic orbits are obtained for different values of therefore classes of universality can be defined for specific values of our mapping acts as the discontinuous map representation of well known nonlinear systems thus making our study broadly applicable also the formalism used is general and the procedure can be extended to characterize many other dynamical systems

processing of acoustic waveforms a sinusoidal model for acoustic waveforms is applied to develop a new analysis synthesis technique which characterizes a waveform by the amplitudes frequencies and phases of component sine waves these parameters are estimated from a short time fourier transform rapid changes in the highly resolved spectral components are tracked using the concept of birth and death of the underlying sine waves the component values are interpolated from one frame to the next to yield a representation that is applied to a sine wave generator the resulting synthetic waveform preserves the general waveform shape and is perceptually indistinguishable from the original furthermore in the presence of noise the perceptual characteristics of the waveform as well as the noise are maintained the method and devices disclosed herein are particularly useful in speech coding time scale modification frequency scale modification and pitch modification

dissipation and its consequences in the scaling exponents for a family of two dimensional mappings the effects and consequences of dissipation in the scaling exponents describing the behaviour of average properties over the chaotic dynamics for a family of two dimensional mappings are studied the mapping is parametrized by an exponent in one of the dynamical variables and by a parameter 0 1 which denotes the amount of the dissipation the lyapunov exponents are obtained for different values of and in the range 0 1 the behaviour of the approaching orbits to the chaotic attractors is described analytically to be of exponential type the deviation around the average action for chaotic orbits was described by a single set of scaling exponents obtained for different leading the model to fall into the same universality class as that of the dissipative bouncer model

analysis of multicomponent lfm signals by a combined wigner hough transform the aim of the paper is the performance evaluation of a method for the analysis of mono or multicomponent linear frequency modulation lfm signals based on the hough transform of the wigner ville distribution of the signals a closed form expression is found for the signal to noise ratio and the parameter estimation accuracy the overall method as any nonlinear method exhibits a threshold effect nevertheless it is shown to be asymptotically efficient and offers a good rejection capability of the cross terms

a family of dissipative two dimensional mappings chaotic regular and steady state dynamics investigation abstract some dynamical properties for a family of two dimensional mappings controlled by three parameters are considered in this paper for null dissipation and depending on the other control parameters diffusion in phase space is observed a connection with the standard mapping is made to determine the range of control parameters leading to unlimited diffusion in the dissipative case for low nonlinearity we obtain the fixed points and an expression to find any periodic orbit with any period if it exists for large nonlinearity we investigate the lyapunov exponents and characterise the steady state of the system for a long time

threshold to global diffusion in a nonmonotonic map with quadratic nonlinearity abstract in this paper the threshold to global diffusion of a nonmonotonic map with quadratic nonlinearity using a forcing function k sin as in the standard map is analyzed for low values of the stochastic parameter k the breaking of the last kam curve is caused by the period one reconnecting resonance at higher k secondary resonances play an increasingly important role two kinds of kam curves are studied those between reconnecting resonances and those outside a reconnecting resonance pair using a perturbative hamiltonian method to determine the resonance width a weak overlap criterion is used to estimate the breaking of the last kam curve outside of the reconnecting islands for some values of the parameters a nonintegrable reconnecting threshold is found above the threshold of global diffusion in this regime the reconnection increases the diffusion coefficient to a value close to the quasilinear value of the standard map

analysis of polynomial phase signals by the integrated generalized ambiguity function the aim of this work is the performance analysis of a method for the detection and parameter estimation of mono or multicomponent polynomial phase signals pps embedded in white gaussian noise and based on a generalized ambiguity function the proposed method is shown to be asymptotically efficient for second order pps and nearly asymptotically efficient for third order ppss the method presents some advantages with respect to similar techniques like the polynomial phase transform for example in terms of i a closer approach to the cramer rao lower bounds ii a lower snr threshold iii a better capability of discriminating multicomponent signals

locating invariant tori for a family of two dimensional hamiltonian mappings departamento de estatistica matemat apl e computaoinstituto de geociencias e ciencias exatas unesp univ estadual paulista av 24a 1515bela vista cep 13506 900 rio claro sp

a subspace approach to adaptive narrow band interference suppression in dsss we address the problem of suppression of a digital narrow band interferer in direct sequence spread spectrum dsss communications we focus on the adaptive suppression method proposed by honig madhow and verdti see ieee trans inform theory vol 41 p 944 960 1995 for wide band interference applying it to a narrow band interferer we identify the eigenspaces of the system dynamics to analyze the convergence of the adaptive version of the minimum mean square error mmse algorithm for this application using this subspace approach we are able to 1 significantly decrease the convergence times via a new constraint on the step size in adaptation 2 introduce a simple parameterization of the mean output energy moe and signal to interference ratio sir to compare performance of various receivers and 3 identify modes of operation where the algorithm will cease to effectively cancel interference we propose a new adaptive receiver that avoids the convergence anomalies identified while capitalizing on the new step size for faster convergence simulation results to support theoretical results are presented

normal forms for 4d symplectic maps with twist singularities we derive a normal form for a near integrable four dimensional 4d symplectic map with a fold or cusp singularity in its frequency mapping the normal form is obtained for when the frequency is near a resonance and the mapping is approximately given by the time t mapping of a two degree of freedom hamiltonian flow consequently there is an energy like invariant the fold hamiltonian is similar to the well studied one degree of freedom case but is essentially non integrable when the direction of the singular curve in action does not coincide with curves of the resonance module we show that many familiar features such as multiple island chains and reconnecting invariant manifolds are retained even in this case the cusp hamiltonian has an essential coupling between its two degrees of freedom even when the singular set is aligned with the resonance module using averaging we approximately reduce this case to one degree of freedom as well the resulting hamiltonian and its perturbation with small cusp angle is analyzed in detail

time frequency projection filters and time frequency signal expansions we consider the problems of designing a linear time varying filter with a specified time frequency tf pass region and of constructing an orthonormal basis for the parsimonious expansion of signals located in a given tf support region these problems of tf filtering and tf signal expansion are reduced to the problem of designing a tf subspace i e a linear signal space comprising all signals located in a given tf legion specifically the tf filter is taken to be the orthogonal projection operator on the tf subspace we present an optimum design of tf subspaces that is based on the wigner distribution of a linear signal space and is an extension of the well known signal synthesis problem the optimum tf subspace is shown to be an eigenspace of the tf region and some properties of eigenspaces are discussed the performance of tf projection filters and tf signal expansions is studied both analytically and via computer simulation

manifold reconnection and diffusion in strong chaos abstract we analyse diffusion across a reconnecting zone in a regime of strong chaos numerical estimates from the angular correlation functions averaged over a suitable set of phase space initial conditions are compared to a local diffusion coefficient obtained using fick s law it emerges that the diffusion coefficient is enhanced from small to larger values as successive reconnection like processes or more usual bifurcations take place this feature is illustrated using a quadratic nontwist map

a graphical representation of protein based on a novel iterated function system abstract in this article a novel family of iterated function system ifs was introduced to outline a 2d graphical representation of protein sequences which incorporates with various physicochemical properties of amino acids then a mathematical description was suggested to quantificationally compare the similarities and dissimilarities of protein sequences from their 2d curves based on this method similarities dissimilarities were compared among sequences of the nd5 proteins of nine different species as well as sequences of eight nd6 proteins the phylogenetic tree of the nine nd5 proteins was constructed according to fuzzy cluster analysis by correlation analysis the clustalw results were compared with our similarity dissimilarity results and other graphical representation results to demonstrate the effectiveness of our approach

3d graphical representation of protein sequences and their statistical characterization abstract based on three physicochemical properties of amino acid side chains we proposed a novel unique 3d graphical representation of protein sequences then we constructed two vectors of three components as mathematical objects to characterize protein sequences numerically the similarity dissimilarity analysis among nine nd5 protein sequences proved the utility of our approach a correlation and significance analysis have been provided to compare our results and the sequence homology

a linearly constrained fast transversal filter for direct sequence spread spectrum interference rejection this paper introduces an improved direct sequence spread spectrum interference rejection filter using the fast transversal filter ftf adaptive algorithm a constraint is imposed on the ftf update resulting in a balance of interference rejection and signal fidelity at the filter output the constraint is controlled by a single parameter

blind adaptive multiuser detection in multipath cdma channels based on subspace tracking a blind adaptive technique for signal demodulation in multipath code division multiple access cdma communication channels is proposed this technique is based on signal subspace estimation the receiver employs a bank of linear filters decorrelating filters or linear mmse filters at the front end to mitigate the multiple access interference and the multipath interference a channel estimator is used to estimate the channel state for diversity combining it is shown that through the use of signal subspace estimation both the decorrelating filterbank and the linear mmse filterbank can be obtained blindly i e they can be estimated from the received signal with the prior knowledge of only the signature waveform of the desired user two forms of the subspace based linear filterbanks are developed and their equivalence in terms of the interference suppression capability is established these subspace based blind adaptive interference suppression techniques require at each symbol epoch the eigenvalues and the eigenvectors of an appropriate signal subspace which ran be obtained using computationally efficient sequential adaptive eigendecomposition subspace tracking algorithms moreover a blind adaptive method for estimating the channel state is developed which also produces the postcombining decision statistic as a byproduct

control of transport in a chaotic lattice abstract we examine a mechanism for the elimination of vertical transport in a square isotropic chaotic lattice we find that applying a shear jet along a line of symmetry in the lattice can completely impede chaotic transport across a specified barrier this is accomplished through a change in allegiance of heteroclinic connections within the lattice this mechanism is relatively insensitive to details such as amplitude or shape of the applied shear it depends quite sensitively however on the precise location of the shear this suggests that the placement of flow control devices in physical situations may be much more critical to transport behavior than are other control parameters in addition we develop a necessary condition for the existence of boundary circles in non twist maps using this condition we find that transport across a barrier can be eliminated for all practical purposes without evidence for an invariant boundary circle

estimation and classification of polynomial phase signals the measurement of the parameters of complex signals with constant amplitude and polynomial phase measured in additive noise is considered a novel new integral transform that is adapted for signals of this type is introduced this transform is used to derive estimation and classification algorithms that are simple to implement and that exhibit good performance the algorithms are extended to constant amplitude and continuous nonpolynomial phase signals

chaotic properties of a time modulated barrier some chaotic properties of a classical particle interacting with a time modulated barrier are studied the dynamics of this problem is obtained by use of a two dimensional nonlinear area preserving map the chaotic low energy region is characterized in terms of lyapunov exponents the time that the particle stays trapped in the well is such that the distributions of successive reflections and of the corresponding successive reflection times obey power laws with the same exponent using time series analysis we show that the chaotic sea exhibits an interesting scaling property over a large range of control parameters our results indicate that the particle experiences unlimited energy growth when the barrier behaves randomly

new nonlinear algorithms for estimating and suppressing narrowband interference in ds spread spectrum systems it has been shown that the narrowband nb interference suppression capability of a direct sequence ds spread spectrum system can be enhanced considerably by processing the received signal via a prediction error filter the conventional approach to this problem makes use of a linear filter however the binary ds signal that acts as noise in the prediction process is highly non gaussian thus linear filtering is not optimal vijayan and poor 1990 first proposed using a nonlinear approximate conditional mean acm filter of the masreliez 1975 type and obtained significant results this paper proposes a number of new nonlinear algorithms our work consists of three parts 1 we develop a decision directed kalman ddk filter that has the same performance as the acm filter but a simpler structure 2 using the nonlinear function in the acm and the ddk filters we develop other nonlinear least mean square lms filters with improved performance 3 we further use the nonlinear functions to develop nonlinear recursive least squares rls filters that can be used independently as predictors or as interference identifiers so that the acm or the ddk filter can be applied simulations show that our nonlinear algorithms outperform conventional ones

another look at the saddle centre bifurcation vanishing twist abstract in the saddle centre bifurcation a pair of periodic orbits is created out of nothing in a hamiltonian system with two degrees of freedom it is the generic bifurcation with multiplier one we show that out of nothing should be replaced by out of a twistless torus more precisely we show that invariant tori of the normal form have vanishing twist right before the appearance of the new orbits vanishing twist means that the derivative of the rotation number with respect to the action for constant energy vanishes we explicitly derive the position of the twistless torus in phase and in parameter space near the saddle centre bifurcation the theory is applied to the area preserving henon map

direct sequence spread spectrum narrowband interference rejection using property restoration a new method of rejecting narrowband interference in direct sequence spread spectrum ds ss communications is presented a typical approach is to reject the interference using a filter with large attenuation at the interference frequencies before despreading the interference rejection method presented incorporates vector space projection techniques to suppress the correlated interference several signal characteristics are formulated which lead to constraint surfaces in the vector space of possible solutions these constraint surfaces describe interference rejection solutions which introduce minimal distortion to the spread spectrum signal and simultaneously remove the interference the constraint surfaces essentially correspond to spread spectrum signal estimates which after interference rejection conform to known characteristics of the transmitted spread spectrum signal the formulation of the surfaces relies on prior knowledge about the spread spectrum signal correlation and spectral properties

an approximate statistical analysis of the widrow lms algorithm with application to narrow band interference rejection the widrow lms algorithm is considered for the implementation of an adaptive prewhitening filter in a direct sequence ds spread spectrum receiver exact expressions for the steady state tapweight covariance matrix and resulting average excess mean square error are developed for the real lms algorithm when the input contains a random binary sequence used to model a pseudonoise spreading sequence it is shown here that the output samples of the adaptive filter possess approximately gaussian statistics under the conditions of slow convergence and a large number of filter taps using this approximation expressions for the resulting bit error rate ber when the adaptive algorithm is used to suppress a fading gone jammer are developed and numerical results obtained from these expressions are compared to simulation results for the ds receiver

probability of error analyses of a bfsk frequency hopping system with diversity under partial band jamming interference part ii performance of square law nonlinear combining soft decision receivers in this paper error probability analyses are performed for a binary frequency shift keying bfsk system employing l hop bit frequency hopping fh spread spectrum waveforms transmitted over a partial band gaussian noise jamming channel the error probabilities for the l hop bit bfsk fh systems are obtained as the performance measure of the square law linear combining soft decision receiver under the assumption of the worst case partial band jamming the receiver in our analysis assumes no knowledge of jamming state side information both exact and approximate multiple bound parameter chernoff bound solutions are obtained under two separate assumptions with and without the system s thermal noise in the analyses numerical results of the error rates are graphically displayed as a function of signal to jamming power ratio with l and signal to noise ratio as parameters all of our results exact and approximate indicated that the higher number of hops per bit produced higher error probabilities as a result of increased combining losses when the square law linear combining soft decision receiver is employed in demodulating the multihop per bit waveform

rescaling invariance and anomalous transport in a stochastic layer the anomalous chaotic transport in a one degree of freedom hamiltonian system subjected to a small time periodic perturbation is investigated strong quasiperiodic dependencies of the statistical properties of the motion on log epsilon are found where epsilon is a perturbation parameter the period log lambda depends on the rescaling parameter lambda which is determined only by the frequency of perturbation and behavior of unperturbed hamiltonian near a saddle point the results confirm and generalize a recently established new universal rescaling property of perturbed motion near a saddle point

generalizing the hough transform to detect arbitrary shapes abstract the hough transform is a method for detecting curves by exploiting the duality between points on a curve and parameters of that curve the initial work showed how to detect both analytic curves 1 2 and non analytic curves 3 but these methods were restricted to binary edge images this work was generalized to the detection of some analytic curves in grey level images specifically lines 4 circles 5 and parabolas 6 the line detection case is the best known of these and has been ingeniously exploited in several applications 7 8 9 we show how the boundaries of an arbitrary non analytic shape can be used to construct a mapping between image space and hough transform space such a mapping can be exploited to detect instances of that particular shape in an image furthermore variations in the shape such as rotations scale changes or figure ground reversals correspond to straightforward transformations of this mapping however the most remarkable property is that such mappings can be composed to build mappings for complex shapes from the mappings of simpler component shapes this makes the generalized hough transform a kind of universal transform which can be used to find arbitrarily complex shapes

short time fractional fourier transform and its applications the fractional fourier transform frft is a potent tool to analyze the chirp signal however it fails in locating the fractional fourier domain frfd frequency contents which is required in some applications the short time fractional fourier transform stfrft is proposed to solve this problem it displays the time and frfd frequency information jointly in the short time fractional fourier domain stfrfd two aspects of its performance are considered the 2 d resolution and the stfrfd support the time frfd bandwidth product tfbp is defined to measure the resolvable area and the stfrfd support the optimal stfrft is obtained with the criteria that maximize the 2 d resolution and minimize the stfrfd support its inverse transform properties and computational complexity are presented two applications are discussed the estimations of the time of arrival toa and pulsewidth pw of chirp signals and the stfrfd filtering simulations verify the validity of the proposed algorithms

leaking of trajectories from the phase space of discontinuous dynamics the escape of particles from the phase space produced by a two dimensional nonlinear and area preserving discontinuous map is investigated by using both numerical simulations and the explicit solution of the corresponding diffusion equation the mapping given in action angle variables is parameterized by k which controls a transition from integrability to non integrability we focus on the two dynamical regimes of the map slow diffusion and quasilinear diffusion regimes separated by the critical parameter value kc 1 when a hole is introduced in the action axis we find the histogram of escape times and the survival probability of particles to be scaling invariant in both the slow and the quasilinear diffusion regimes with scaling laws proportional to the corresponding diffusion coefficients namely proportional to and k2 respectively our numerical simulations agree remarkably well with the analytical results obtained from the explicit solution of the diffusion equation hence giving robustness to the escape formalism

narrow band interference suppression in multiuser cdma systems this paper handles the simultaneous suppression of narrow band and multiaccess interference in code division multiple access cdma direct sequence spread spectrum dsss systems the basic structure we refer to is reminiscent of the decorrelating detector but here the design strategy relies on the concept of combating jointly the two interference sources precisely a decision as to the bit transmitted by each user is made based on the projection of the observables onto the orthogonal complement to the subspace spanned by the other users signatures and the narrow band interference we focus on several different implementations of such a strategy assuming a different degree of prior knowledge as to the narrow band interference an important side result of the proposed approach is that in general complete suppression of data like interference may be achieved through periodically time varying processing an adaptive version of such a receiver is also presented wherein the projection direction is estimated based on suitable estimates of the covariance properties of the observables the value of this method is also assessed by studying the rate of convergence of the estimated direction to the true projection direction

finding critical exponents for two dimensional hamiltonian maps two dimensional nonlinear area preserving mappings have been considered in the study of dynamical systems for many years applications of this formalism can be used in study of channel flows waveguide transport properties fermi acceleration and also for the study of magnetic field lines in toroidal plasma devices with reversed shear such as tokamaks1 10 generally such kind of mappings have one or more control parameters they can control the intensity of the nonlinearity controlling also a transition from integrability to nonintegrability the phase space of these mappings exhibit quite often mixed forms one can observe a large chaotic sea that eventually surrounds kolmogorov arnold moser islands and is limited by a set of invariant tori the size of the chaotic sea is strongly influenced by the control parameters since they play the rule of controlling the intensity of the nonlinearity in this paper we address specifically a transition from integrability to nonintegrability present in a special class of two dimensional nonlinear area preserving mappings we look at average properties along the chaotic sea and therefore we find critical exponents that describe the behavior of average quantities of the chaotic sea such quantities are described in terms of scaling arguments leading to a generic and robust description of a scaling observed for the chaotic sea the critical exponents are obtained for several values of the control parameters the knowledge of such exponents allow us to define and compare classes of universality for the two dimensional hamiltonian mappings the paper is organized as follows in sec ii we present the model and discuss the variables and control parameters used some properties of the phase space are also discussed including a characterization of fixed points the chaotic component of the phase space is characterized by lyapunov exponents in sec iii we obtain and describe the critical exponents that define classes of universality a merger of all the curves of the average quantity is obtained finally in the sec iv we present our concluding remarks ii definition of the problem and the mapping in this section we present and discuss some dynamical properties for a set of two dimensional hamiltonian mappings we assume that there is a two dimensional integrable system that is slightly perturbed the hamiltonian function that in principle describes the system is written as 11

blind source separation based on time frequency signal representations blind source separation consists of recovering a set of signals of which only instantaneous linear mixtures are observed thus far this problem has been solved using statistical information available on the source signals this paper introduces a new blind source separation approach exploiting the difference in the time frequency t f signatures of the sources to be separated the approach is based on the diagonalization of a combined set of spatial t f distributions in contrast to existing techniques the proposed approach allows the separation of gaussian sources with identical spectral shape but with different t f localization properties the effects of spreading the noise power while localizing the source energy in the t f domain amounts to increasing the robustness of the proposed approach with respect to noise and hence improved performance asymptotic performance analysis and numerical simulations are provided

scaling properties of a simplified bouncer model and of chirikov s standard map scaling properties of chirikov s standard map are investigated by studying the average value of i2 where i is the action variable for initial conditions in a the stability island and b the chaotic component scaling behavior appears in three regimes defined by the value of the control parameter k i the integrable to non integrable transition k 0 and k kc kc 0 9716 ii the transition from limited to unlimited growth of i2 k kc iii the regime of strong nonlinearity k kc our scaling results are also applicable to pustylnikov s bouncer model since it is globally equivalent to the standard map we also describe the scaling properties of a stochastic version of the standard map which exhibits unlimited growth of i2 even for small values of k

performance analysis of narrow band interference rejection techniques in ds spread spectrum systems linear least squares estimation llse techniques can provide an effective means of suppressing narrow band interference in direct sequence ds spread spectrum systems in the results presented here analytical expressions for bit error rate are derived for two ds spread spectrum systems under the conditions of either tone or narrowband gaussian interference it is shown that the most common llse filter design can lead to performance inferior to that of various other filter designs however results are also presented demonstrating that an llse filter design motivated by the structure of the maximum likelihood receiver leads to consistently superior performance the performance of a system using this new design criterion is compared with that of an approximation to the maximum likelihood ml receiver for the tone interference model and with that of the exact ml receiver for the gaussian interference finally it is shown that the bit error rate estimate obtained from application of a gaussian approximation for the test statistic is overly pessimistic for the systems studied here

interference mitigation in spread spectrum communication systems using time frequency distributions the capability of the time frequency distributions tfds to properly represent a single as well as multiple component signals in time and frequency permits the application of a new approach for interference excision in spread spectrum communication systems the instantaneous frequency if estimate from the tfd is used to construct a finite impulse response filter that reduces the interference power with a minimum possible distortion of the desired signal the proposed technique is therefore a case of open loop adaptive filtering three and five coefficient zero phase excision filters are considered closed form expressions of the improvement of snr at the receiver correlator output using the tfd based adaptive filtering are derived for two extreme cases of time varying interferers namely those of fixed frequency sinusoids and randomly changing instantaneous frequencies simulation results including the bit error rates are presented for both swept and frequency hopping jammers

method and apparatus for fundamental frequency extraction or detection in speech an object is to provide a method of extracting sound source information which method enables the characteristics of fixed points of mapping from filter center frequency to output instantaneous frequency to be detected from instantaneous data as a value which can be interpreted quantitatively in a method of extracting sound source information by use of fixed points of mapping from frequency to instantaneous frequency instantaneous frequency of each filter 2 9 is partial differentiated with respect to frequency by an instantaneous frequency frequency differentiation circuit 3 10 to thereby obtain a first value output of each filter is partial differentiated with respect to frequency and then with respect to time by an instantaneous frequency time frequency differentiation circuit 4 11 to thereby obtain a second value and proper weights are imparted to the first and second values and short time weighted integration with respect to time is performed by a carrier to noise ratio calculation circuit 5 12 to estimate a carrier to noise ratio of each filter thus a carrier to noise ratio is obtained and an estimated value of evaluation value is obtained

maximum likelihood localization of multiple sources by alternating projection an algorithm referred to as apm for computing the maximum likelihood estimator of the locations of simple sources in passive sensor arrays is presented the algorithm is equally applicable to the case of coherent signals and to the case of a single snapshot the algorithm is iterative the maximum of the likelihood function is computed by successive approximations the convergence of the algorithm to the global maximum is demonstrated for a variety of scenarios the key to this global convergence is the initialization scheme

short time fourier transform receiver for nonstationary interference excision in direct sequence spread spectrum communications a new adaptive excision approach for nonstationary interference excision in direct sequence spread spectrum ds ss communications is introduced the proposed excision approach is based on the attractive localization properties of the impulse responses of the multiple pole filters these impulse responses have gaussian like shapes and decrease in bandwidth with higher pole multiplicities when used as data windows they field a large class of computationally efficient short time fourier transforms stfts localization measures can be applied to determine the optimum window that maximally concentrates the interference in the time frequency t f domain interference mitigation is then achieved by applying a binary excision mask to the corresponding stft for each data bit we show that the proposed interference excision method permits both data dependent windowing and time varying filtering and leads to improved ber performance of the ds ss system the paper also derives the general optimum receiver implementing the stft based interference excision system

a rescaling of the phase space for hamiltonian map in this work we study a rescale of the phase space in a family of two dimensional nonlinear hamiltonian mapping the mapping considered is parametrised by kepler map and mappings with diverging angles in the limit of vanishing action are recovered the transition from local to global chaos is used the chaotic sea is scaling invariant universality classes are defined a rescale of the phase space for a family of two dimensional nonlinear hamiltonian mappings was made by using the location of the first invariant kolmogorov arnold moser kam curve average properties of the phase space are shown to be scaling invariant and with different scaling times specific values of the control parameters are used to recover the kepler map and the mapping that describes a particle in a wave packet for the relativistic motion the phase space observed shows a large chaotic sea surrounding periodic islands and limited by a set of invariant kam curves whose position of the first of them depends on the control parameters the transition from local to global chaos is used to estimate the position of the first invariant kam curve leading us to confirm that the chaotic sea is scaling invariant the different scaling times are shown to be dependent on the initial conditions the universality classes for the kepler map and mappings with diverging angles in the limit of vanishing action are defined

vanishing twist in the hamiltonian hopf bifurcation the hamiltonian hopf bifurcation has an integrable normal form that describes the passage of the eigenvalues of an equilibrium through the 1 1 resonance at the bifurcation the pure imaginary eigenvalues of the elliptic equilibrium turn into a complex quadruplet of eigenvalues and the equilibrium becomes a linearly unstable focus focus point we explicitly calculate the frequency map of the integrable normal form in particular we obtain the rotation number as a function on the image of the energy momentum map in the case where the fibres are compact we prove that the isoenergetic non degeneracy condition of the kam theorem is violated on a curve passing through the focus focus point in the image of the energy momentum map this

periodic chaotic billiards quantum classical correspondence in energy space we investigate the properties of eigenstates and local density of states ldos for a periodic two dimensional rippled billiard focusing on their quantum classical correspondence in energy representation to construct the classical counterparts of ldos and the structure of eigenstates ses the effects of the boundary are first incorporated via a canonical transformation into an effective potential rendering the one particle motion in the 2d rippled billiard equivalent to that of two interacting particles in 1d geometry we show that classical counterparts of ses and ldos in the case of strong chaotic motion reveal quite a good correspondence with the quantum quantities we also show that the main features of the ses and ldos can be explained in terms of the underlying classical dynamics in particular of certain periodic orbits on the other hand statistical properties of eigenstates and ldos turn out to be different from those prescribed by random matrix theory we discuss the quantum effects responsible for the nonergodic character of the eigenstates and individual ldos that seem to be generic for this type of billiards with a large number of transverse channels

robust attractor of non twist systems abstract we present a new kind of one dimensional attractor which has not yet been predicted in the non linear dynamics theory we consider a non linear map which presents typical non twist manifestations as isochronous resonances and shearless torus it is known that this torus corresponds to a very sturdy barrier in the phase space of some area preserving systems we show that when dissipation is present in the system the shearless curve carries its robustness to the dissipative scenario it becomes a powerful attractor which we call shearless attractor which is persistent under the variation of the parameters and it exchanges its stability from chaotic to quasi periodic or vice versa depending on the set of parameters

a new graphical representation of protein sequences and its applications abstract sequence analysis is one of the foundations in bioinformatics for the abundant information hidden in the sequences it is helpful for scientists study on the function of dna proteins and cells in this paper we outline a novel method for protein sequences similarity analysis based on the physical chemical properties of amino acids we consider the protein sequence as a rigid body with mass then we introduce the moment of inertia to the calculation of similarity of sequences and the sequences are transformed into vectors by the tensor for moment of inertia the euclidean distance is employed as a measurement of the similarities at last the comparison with other references results shows our approach is reasonable and effective

system identification using chirp signals and time variant filters in the joint time frequency domain we propose a novel method to identify an unknown linear time invariant lti system in low signal to noise ratio snr environment the method is based on transmitting chirp signals for the transmitter and using linear time variant filters in the joint time frequency tf domain for the receiver to reduce noise before identification due to the tf localization property of chirp signals a large amount of additive white noise can be reduced and therefore the snr before identification can be significantly increased this however cannot be achieved in the conventional methods where pseudo random signals are used and therefore noise reduction techniques do not apply our simulation results indicate that the method proposed outperforms the conventional methods significantly in a low snr environment this paper provides a good application of time frequency analysis and synthesis