detection of signals by information theoretic criteria a new approach is presented to the problem of detecting the number of signals in a multichannel time series based on the application of the information theoretic criteria for model selection introduced by akaike aic and by schwartz and rissanen mdl unlike the conventional hypothesis testing based approach the new approach does not requite any subjective threshold settings the number of signals is obtained merely by minimizing the aic or the mdl criteria simulation results that illustrate the performance of the new method for the detection of the number of signals received by a sensor array are presented

reversible jump mcmc for joint detection and estimation of sources in colored noise this paper presents a novel bayesian solution to the difficult problem of joint detection and estimation of sources impinging on a single array of sensors in spatially colored noise with arbitrary covariance structure robustness to the noise covariance structure is achieved by integrating out the unknown covariance matrix in an appropriate posterior distribution the proposed procedure uses the reversible jump markov chain monte carlo mcmc method to extract the desired model order and direction of arrival parameters we show that the determination of model order is consistent provided a particular hyperparameter is within a specified range simulation results support the effectiveness of the method

computational modeling of localized failure in solids xfem vs pf czm abstract this work addressesnumerical comparison between the extended finite element method xfem and the phase field regularized cohesive zone model pf czm wu 2017 2018a for the modeling of cohesive fracture induced localized failure in solids a novel implementation of the pf czm is proposed similarly to the xfem in which the added degrees of freedom characterizing the crack behavior are associated only with those nodes within a small sub domain representative benchmark examples show that both methods are independent of the mesh discretization for problems with the crack path known a priori both methods give almost coincident numerical results though the xfem is advantageous due to its high coarse mesh resolution for complex problems with arbitrary crack propagation even though some discrepancies are observed the numerical results given by both methods are also quantitatively similar if the predicted crack trajectories are close to each other despite the higher computational cost in this case the pf czm is much more favored due to its intrinsic capability of modeling complex crack configurations e g nucleation propagation merging and branching etc with no need of any extra strategy the above facts validate our previous theoretical analysis that the pf czm approaches asymptotically to a discontinuous czm for a vanishing length scale as it avoids most challenging issues exhibited by other approaches the pf czm is not only theoretically elegant but also numerically appealing for the modeling of localized failure in solids

performance of precoded ofdm with channel estimation error pair wise error probability pep is analyzed in the presence of channel estimation error cee for group linear constellation precoded orthogonal frequency division multiplexing glcp ofdm it is observed that the cee does not reduce the diversity order but contributes to a loss of coding gain furthermore the proposed optimal power allocation scheme based on the derived pep has performance that converges to the performance with perfect channel state information when the number of subcarriers to the channel length ratio increases

tracking performance of least squares mimo channel estimation algorithm in this paper the tracking performance analysis of the least squares ls multiple input multiple output mimo channel estimation and tracking algorithm is presented mimo channel estimation is a novel application of the ls algorithm that presents near optimum performance by karami and shiva in 2003 and 2006 in this paper the mean square error mse of tracking of the ls mimo channel estimator algorithm is derived as a closed form function of the doppler shift forgetting factor channel rank and the length of training sequences in the analysis all training symbols are considered as randomly generated equal power vectors on the unit circle or in other words phase shift keying psk signaling by evaluating this function some insights into the tracking behavior of the ls mimo channel estimator are achieved then the calculated tracking error is compared with the tracking error derived from monte carlo simulation for quaternary psk based training signals to verify the validation of the presented analysis finally the optimum forgetting factor is derived to minimize the error function and it is shown that the optimum forgetting factor is highly dependent on the training length doppler shift and eb no also it is concluded that in low eb no values the number of transmitter antennas has negligible effect on the optimal value of the forgetting factor

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

damage growth modeling using the thick level set tls approach efficient discretization for quasi static loadings the thick level set tls model is a damage model containing a non local treatment that prevents from spurious localization issues it also offers an automatic transition from damage to fracture the tls approach to model damage growth was first presented in moes et al 24 with a first numerical implementation for a time dependent damage evolution law in this paper we propose some improvements in terms of discretization and explicit damage growth algorithms to obtain a robust efficient and easy to implement model these improvements include a simple and efficient variational formulation for computing the non local quantities as well as the introduction of a so called ramped heaviside enrichment function to properly take into account the transition to cracks in fully damaged zones we consider here a simple explicit formulation for quasi static loadings decoupling the elastic computation and the damage growth the method is validated through standard benchmarks and compared to the griffith s fracture theory the convergence of energy and displacement errors is observed more complex computations including damage initiations are eventually performed

an extended finite element method with analytical enrichment for cohesive crack modeling a recent approach to fracture modeling has combined the extended finite element method xfem with cohesive zone models most studies have used simplified enrichment functions to represent the strong discontinuity but have lacked an analytical basis to represent the displacement gradients in the vicinity of the cohesive crack in this study enrichment functions based upon an existing analytical investigation of the cohesive crack problem are proposed these functions have the potential of representing displacement gradients in the vicinity of the cohesive crack and allow the crack to incrementally advance across each element key aspects of the corresponding numerical formulation and enrichment functions are discussed a parameter study for a simple mode i model problem is presented to evaluate if quasi static crack propagation can be accurately followed with the proposed formulation the effects of mesh refinement and mesh orientation are considered propagation of the cohesive zone tip and crack tip time variation of the cohesive zone length and crack profiles are examined the analysis results indicate that the analytically based enrichment functions can accurately track the cohesive crack propagation of a mode i crack independent of mesh orientation a mixed mode example further demonstrates the potential of the formulation copyright 2008 john wiley sons ltd

modelling of cohesive crack growth in concrete structures with the extended finite element method in this paper the extended finite element method xfem is used for a discrete crack simulation of concrete using an adaptive crack growth algorithm different criteria for predicting the direction of the extension of a cohesive crack are investigated in the context of the xfem the robustness of these criteria is analyzed with reference to three examples and the results are compared to experiments furthermore the efficient application of the quadtree data structure for an iterative mesh refinement in combination with the xfem is shown considerably to reduce the computational effort

everything you always wanted to know about training guidelines derived using the affine precoding framework and the crb in this paper affine precoding is used to investigate the tradeoffs that exist while using the transmitter resources on training versus information symbols the channel input is a training vector superimposed on a linearly precoded vector of symbols a block fading frequency selective multi input multi output mimo channel is considered to highlight the tradeoffs between training and data symbols the fisher information matrix fim is derived under two circumstances the random parameter vector to be estimated contains 1 only fading channel coefficients and 2 unknown data symbols as well as the channel coefficients while strategy 1 corresponds to the receiver structure in which the channel is estimated initially and the channel measurement is utilized to retrieve the data symbols strategy 2 corresponds to the structure in which channel and symbol estimations are performed jointly the interesting outcome of the study in this paper is that minimizing the channel cramer rao bound crb for strategies 1 and 2 under a total average transmit power constraint leads to different affine precoder design guidelines

cohesive and non cohesive fracture by higher order enrichment of xfem summary a comprehensive study is performed on the use of higher order terms of the crack tip asymptotic fields as enriching functions for the extended fem xfem for both cohesive and traction free cracks for traction free cracks the williams asymptotic field is used to obtain highly accurate stress intensity factors sifs directly from the enriched degrees of freedom without any post processing the low accuracy of the results of the original research on this subject by liu et al int j numer meth engng 2004 59 1103 1118 is remedied here by appropriate modifications of the enrichment scheme the modifications are simple and can be easily included into an xfem computer code for cohesive cracks the relevant asymptotic field is used and two widely used criteria including the sifs criterion and the stress criterion are examined for the crack growth simulation both linear and nonlinear cohesive laws are used for the stress criterion averaging is avoided due to the highly accurate crack tip approximation because of the higher order enrichment then a modified stress criterion is proposed which is shown to be applicable to a wider class of problems several numerical examples including straight and curved cracks stationary and growing cracks single and multiple cracks and traction free and cohesive cracks are studied to investigate in detail the robustness and efficiency of the proposed enrichment scheme copyright 2012 john wiley sons ltd

the extended generalized finite element method an overview of the method and its applications an overview of the extended generalized finite element method gefm xfem with emphasis on methodological issues is presented this method enables the accurate approximation of solutions that involve jumps kinks singularities and other locally non smooth features within elements this is achieved by enriching the polynomial approximation space of the classical finite element method the gefm xfem has shown its potential in a variety of applications that involve non smooth solutions near interfaces among them are the simulation of cracks shear bands dislocations solidification and multi field problems copyright 2010 john wiley sons ltd

fading channels how perfect need perfect side information be the analysis of flat fading channels is often performed under the assumption that the additive noise is white and gaussian and that the receiver has precise knowledge of the realization of the fading process these assumptions imply the optimality of gaussian codebooks and of scaled nearest neighbor decoding here we study the robustness of this communication scheme with respect to errors in the estimation of the fading process we quantify the degradation in performance that results from such estimation errors and demonstrate the lack of robustness of this scheme for some situations we suggest the rule of thumb that in order to avoid degradation the estimation error should be negligible compared to the reciprocal of the signal to noise ratio snr

on the capacity and energy efficiency of training based transmissions over fading channels in this paper the capacity and energy efficiency of training based communication schemes employed for transmission over a priori unknown rayleigh block fading channels are studied initially the case in which the product of the estimate error and transmitted signal is assumed to be gaussian noise is considered in this case it is shown that bit energy requirements grow without bound as the signal to noise ratio snr goes to zero and the minimum bit energy is achieved at a nonzero snr value below which one should not operate the effect of the block length on both the minimum bit energy and the snr value at which the minimum is achieved is investigated flash training and transmission schemes are analyzed and shown to improve the energy efficiency in the low snr regime in the second part of this paper the capacity and energy efficiency of training based schemes are investigated when the channel input vector in each coherence block is subject to peak power constraints the capacity achieving input structure is characterized and the magnitude distribution of the optimal input is shown to be discrete with a finite number of mass points the capacity bit energy requirements and optimal resource allocation strategies are obtained through numerical analysis the improvements in energy efficiency when on off keying ook with fixed peak power and vanishing duty cycle is employed are studied

a finite element method with mesh separation based approximation technique and its application in modeling crack propagation with adaptive mesh refinement summary this paper presents a fem with mesh separation based approximation technique that separates a standard element into three geometrically independent elements a dual mapping scheme is introduced to couple them seamlessly and to derive the element approximation the novel technique makes it very easy for mesh generation of problems with complex or solution dependent varying geometry it offers a flexible way to construct displacement approximations and provides a unified framework for the fem to enjoy some of the key advantages of the hansbo and hansbo method the meshfree methods the semi analytical fems and the smoothed fem for problems with evolving discontinuities the method enables the devising of an efficient crack tip adaptive mesh refinement strategy to improve the accuracy of crack tip fields both the discontinuities due to intra element cracking and the incompatibility due to hanging nodes resulted from the element refinement can be treated at the elemental level the effectiveness and robustness of the present method are benchmarked with several numerical examples the numerical results also demonstrate that a high precision integral scheme is critical to pass the crack patch test and it is essential to apply local adaptive mesh refinement for low fracture energy problems copyright 2014 john wiley sons ltd

optimal training signals for mimo ofdm channel estimation in the presence of frequency offset and phase noise we develop robust mean square error mse optimal training signal designs for multiple input multiple output orthogonal frequency division multiplexing channel estimation with frequency offset and phase noise pn and present analytical and simulation results for the frequency offset and pn effects on channel estimation the proposed designs are more advantageous for moderate to high values of signal to noise ratio snr residual frequency offset and pn level at snr 10 db the normalized mse reductions of our proposed training signals at normalized frequency offset v 0 1 0 5 are about 9 and 19 db respectively for one transmit antenna and 6 and 11 db for two transmit antennas

extended isogeometric analysis for cohesive fracture the objective of this study is to present an extended isogeometric formulation for cohesive fracture the approach exploits the higher order interelement continuity property of nonuniform rational b splines nurbs in particular the higher accuracy that results for the stress prediction which yields an improved estimate for the direction of crack propagation compared to customary lagrangian interpolations shifting is used to ensure compatibility with the surrounding discretization where different from extended finite element methods the affected elements stretch over several rows perpendicular to the crack path to avoid fine meshes around the crack tip in case of cohesive fracture a blending function is used in the extension direction of the crack path to comply with standard finite element data structures bezier extraction is used the absence of the kronecker delta property in the higher order interpolations of isogeometric analysis impedes the enrichment scheme and compatibility enforcement these issues are studied comprehensively at the hand of several examples while crack propagation analyses show the viability of the approach

maximum likelihood estimation for array processing in colored noise direction of arrival estimation of multiple sources using a uniform linear array in noise with unknown covariance is considered the noise is modeled as a spatial autoregressive process with unknown parameters both stochastic and deterministic signal models are considered for the random signal case an approximate maximum likelihood estimator of the signal and noise parameters is derived it requires numerical maximization of a compressed likelihood function over the unknown arrival angles analytical expressions for the mles of the signal covariance and the ar parameters are given similar results for the case of deterministic signals are also presented

assumed enhanced strain and the extended finite element methods a unification of concepts abstract we present strong and weak forms of boundary value problems for a solid with a cohesive frictional crack two commonly used techniques for enhancing the finite element fe interpolation are considered the assumed enhanced strain aes and the extended fe methods we compare and contrast the fe approximations involved in these techniques the aes method employs a piecewise constant interpolation of slip that is discontinuous across element boundaries in contrast the extended fe method interpolates slip continuously across element boundaries through numerical examples we discuss the implications of these approximations to the calculated overall deformation field in the regime of infinitesimal deformation with only a heaviside enrichment we find the aes method to predict larger slip i e softer response compared to the extended fe solution we ascribe the discrepancy to the lack of higher order crack tip enhancement in the extended fe solution finally we compare the slip predicted by the above fe enhancement techniques to that calculated by classical nonlinear contact mechanics algorithm for the case where the crack traverses the element sides

bayesian detection and estimation of cisoids in colored noise the problem of estimating the number of cisoids in colored noise is addressed it is assumed that the noise can be modeled by an autoregression whose order has also to be estimated a new criterion is proposed for estimating the number of cisoids and the autoregressive model order as well as a new algorithm for estimating the cisoidal frequencies in the derivation a bayesian methodology and subspace decomposition are employed the proposed criterion significantly outperforms the popular mdl and aic as applied in a paper by nagesha and kay in addition an algorithm that reduces the computational complexity of the solution is developed computer simulations that demonstrate the performance of the criterion are included

the intersymbol interference channel lower bounds on capacity and channel precoding loss the discrete time additive gaussian intersymbol interference isi channel with i i d not necessarily gaussian input signals is considered several new and old lower bounds on the capacity are derived in a unified manner by assuming different front end receiver filters in particular the sampled whitened matched filter swmf and the minimum mean squared error decision feedback equalizer mmse dfe filter the features of the bounds are demonstrated and compared in several examples with binary and quaternary input signals it is also shown that the effect of an ideal post cursor or tail cancellation in an information preserving context depends primarily on the front end filter while as is well known ideal post cursor cancellation at the output of the swmf decreases the information the opposite trend is seen when an mmse dfe front filter is considered this observation reflects the basic theoretical obstacles in precoding i e ideal post cursor cancellation in the presence of a pre cursor it is used to assess the inherent loss in terms of information rates as compared to the rates achievable with the hypothetical ideal post cursor cancellation associated with any post cursor cancellation technique such as precoding dfe or other variants when operating in synergy with the mmse dfe front end filter the effect of the front end filter on an ideally interleaved precoded coded modulation system is also addressed

coded sampling bound how much training is needed for iterative semi blind channel estimation coherent detection is commonly facilitated by means of pilot aided channel estimation while this approach offers a high estimation accuracy the spectral and power efficiencies are reduced due to the pilot overhead in the case that redundancy due to channel coding is not used for the purpose of channel estimation the maximum pilot spacing for which a time varying channel can be reconstructed without distortion is given by the nyquist shannon sampling theorem in this paper it is shown that if channel coding is taken into account for channel estimation in an iterative fashion the maximum spacing can be significantly extended which results in an increased spectral efficiency towards this goal a so called coded sampling bound is derived this semi analytical bound is compared with the nyquist shannon sampling theorem the presented results indicate that the maximum pilot spacing can be arbitrarily large given a suitable channel code and code rate

embedded interfaces by polytope fem in this paper the polytope finite element method is employed to model an embedded interface through the body independent of the background fem mesh the elements that are crossed by the embedded interface are decomposed into new polytope elements which have some nodes on the interface line the interface introduces discontinuity into the primary variable strong or into its derivatives weak both strong and weak discontinuities are studied by the proposed method through different numerical examples including fracture problems with traction free and cohesive cracks and heat conduction problems with dirichlet and dirichlet neumann types of boundary conditions on the embedded interface for traction free cracks which have tip singularity the nodes near the crack tip are enriched with the singular functions through the extended finite element method the concept of natural element coordinates necs is invoked to drive shape functions for the produced polytopes a simple treatment is proposed for concave polytopes produced by a kinked interface and also for locating crack tip inside an element prior to using the singularity enrichment the proposed method pursues some implementational details of extended generalized finite element methods for interfaces but here the additional dofs are constructed on the interface lines in contrast to x g fem which attach enriched dofs to the previously existed nodes copyright 2011 john wiley sons ltd

construction of polygonal interpolants a maximum entropy approach in this paper we establish a link between maximizing information theoretic entropy and the construction of polygonal interpolants the determination of shape functions on n gons n 3 leads to a non unique under determined system of linear equations the barycentric co ordinates i which form a partition of unity are associated with discrete probability measures and the linear reproducing conditions are the counterpart of the expectations of a linear function the i are computed by maximizing the uncertainty h 1 2 n i log i subject to the above constraints the description is expository in nature and the numerical results via the maximum entropy maxent formulation are compared to those obtained from a few distinct polygonal interpolants the maximum entropy formulation leads to a feasible solution for i in any convex or non convex polygon this study is an instance of the application of the maximum entropy principle wherein least biased inference is made on the basis of incomplete information copyright 2004 john wiley sons ltd

gaussian codes and weighted nearest neighbor decoding in fading multiple antenna channels we investigate the fading multiple antenna channel the decoder is assumed to possess imperfect channel fading information a modified nearest neighbor decoder with an innovative weighting factor is introduced and an expression for the generalized mutual information gmi the achievable rate is obtained we show that under certain conditions the achievable rate is equivalent to that of a fading multiple antenna gaussian channel where fading is known to the receiver and is equal to the channel estimation and where noise is due to both the channel noise and the channel estimation error we show that for our communication scheme the minimum mean square error mmse channel estimator is optimal in the sense that it achieves the highest value of gmi and hence the highest communication rate additionally a training based multiple input multiple output mimo scheme in a block fading channel is investigated and it is shown that the number of degrees of freedom depends on the signal to noise ratio snr

a geometrically regularized gradient damage model with energetic equivalence abstract aiming to bridge the gap between damage and fracture mechanics for modeling localized failure in solids this paper addresses a novel geometrically regularized gradient damage model with energetic equivalence for cracking evolution with the free energy potential defined as usual in terms of the local strain and damage fields the constitutive relations are derived consistently from the standard framework of thermodynamics upon the sharp crack topology geometrically regularized by the damage localization band with a length scale the ensuing energetic equivalence naturally yields the damage evolution law of gradient type and the associated boundary condition of neumann type compared to other gradient damage models no extra assumptions like the nonlocal energy residual and insulation condition are introduced moreover the damage gradient physically accounting for microscopic nonlocal interactions is fully dissipative as expected in line with the unified phase field theory recently proposed by the author wu 2017 during failure processes the material behavior is uniquely characterized by two constitutive functions i e the degradation function defining the free energy potential of the bulk and the geometric function regularizing the sharp crack topology in particular optimal constitutive functions defining an equivalent cohesive zone model of general softening laws are postulated with the involved parameters calibrated from standard material properties the proposed model is numerically implemented into the multi field finite element method and applied to several benchmark tests of concrete under mode i and mixed mode failure it is found that the incorporated length scale can be regarded either a numerical parameter or a material property for the former considered in this work the length scale has negligible if not no effects on the global responses so long as the sharp crack topology and the damage field of high gradients within the localization band are well resolved furthermore the localization bandwidth does not exhibit spurious widening but rather it approaches to a finite value proportional to the length scale comparison between the numerical and experimental results regarding the curve of load versus displacement and crack path confirms validity of the proposed gradient damage model for characterizing localized failure in quasi brittle solids

calculation of fracture mechanics parameters for an arbitrary three dimensional crack by the equivalent domain integral method summary in this paper an equivalent domain integral edi method and the attendant numerical algorithms arc presented for the computation of a near crack tip field parameter the vector je integral and its variation along the front of an arbitrary three dimensional crack in a structural component account is taken of possible non elastic strains present in the structure in this case the near tip je values may be significantly different from the far field values jf especially under non proportional loading

superimposed training for ofdm a peak to average power ratio analysis orthogonal frequency division multiplexing ofdm transmission with superimposed training is considered in this paper one major disadvantage of ofdm is the significant amplitude fluctuations i e high peak to average power ratios pars high pars require large backoff of the average operating power of a radio frequency rf power amplifier pa in order to linearly amplify the signal thus reducing the dc to rf power conversion efficiency the par of the ofdm signal is examined with superimposed training and its complementary cumulative distribution function ccdf is derived achievable lower and upper bounds on the ccdf are also determined in addition the par change is linked to the effective signal to noise ratio snr and thus the bit error rate ber performance under the fixed dc power constraint simulation results are presented to illustrate the proposed par and power analysis for ofdm with superimposed training

estimation of the number of signals in the presence of unknown correlated sensor noise a method for estimating the number of transmitted signals in the presence of spatially correlated sensor noise is proposed the procedure is developed under the assumption that the unknown noise covariance matrix is a band matrix in practice it is quite robust with respect to this finite correlation length assumption in sensor array processing this amounts to assuming that the noise field is locally correlated spatially since spatial stationarity of the noise is not necessary it also applies for instance to white noise with different power along the array simulations indicate that the asymptotic analysis holds for quite small sample sizes

a simple method for crack growth in mixed mode with x fem abstract in this paper a new method for level set update is proposed in the context of crack propagation modeling with the extended finite element method x fem and level sets compared with the existing methods such as the resolution of the hamilton jacobi equations this new method is much simpler because it does not required complex manipulations of the level sets this method called the projection method uses both a classical discretization of the surface of the crack segments for 2d cracks and triangles for 3d cracks and a level set representation of the crack this discretization is updated with respect to the position of the new crack front then the level sets are re computed using the true distance to the new crack by an orthogonal projection of each node of the structure onto the new crack surface then numerical illustrations are given on 2d and 3d academic examples finally three illustrations are given on 3d industrial applications

non planar 3d crack growth by the extended finite element and level sets part i mechanical model a methodology for solving three dimensional crack problems with geometries that are independent of the mesh is described the method is based on the extended finite element method in which the crack discontinuity is introduced as a heaviside step function via a partition of unity in addition branch functions are introduced for all elements containing the crack front the branch functions include asymptotic near tip fields that improve the accuracy of the method the crack geometry is described by two signed distance functions which in turn can be defined by nodal values consequently no explicit representation of the crack is needed examples for three dimensional elastostatic problems are given and compared to analytic and benchmark solutions the method is readily extendable to inelastic fracture problems copyright 2002 john wiley sons ltd

leveraging coherent space time codes for noncoherent communication via training training codes are introduced for the multiple antenna noncoherent multiple block rayleigh fading channel in which the fading coefficients which are constant over a fixed number of dimensions coherence interval for each block and then change independently to a new realization are known neither at the transmitter nor at the receiver each codeword of a training code consists of a part known to the receiver used to form a minimum mean squared error mmse estimate of the channel and a part that contains codeword s of a space time block or trellis code designed for the coherent channel in which the receiver has perfect knowledge of the channel the channel estimate is used as if it were error free for decoding the information bearing part of the training codeword training codes are hence easily designed to have high rate and low decoding complexity by choosing the underlying coherent code to have high rate and to be efficiently decodable conditions for which the estimator detector e d receiver is equivalent to the optimal noncoherent receiver are established a key performance analysis result of this paper is that the training codes when decoded with the e d receiver achieve a diversity order of the error probability that is equal to the diversity order of the underlying coherent code in some cases the performance of training codes can be measured relative to coherent reception via training efficiency which is then optimized over the energy allocation between the training and data phases in the limit of increasing block lengths training codes always achieve the performance of coherent reception the examples of training codes provided in this work have polynomial complexity in rate but an error rate comparable to the best performing unitary designs available even though the latter require exponential decoding complexity

statistical analysis of the performance of information theoretic criteria in the detection of the number of signals in array processing the performances of the akaike 1974 information criterion and the minimum descriptive length criterion methods are examined the events which lead to erroneous decisions are considered and on the basis of these events the probabilities of error for the two criteria are derived the probabilities of the first two events are derived based on the asymptotic distribution of the sample eigenvalues of an estimated hermitian matrix it is further shown that the probabilities of missing and false alarm for these two criteria can be evaluated to a close approximation although the derivation of the probabilities of error is based on an asymptotic analysis the results are confirmed to be in very close agreement with computer simulation results

design and analysis of successive decoding with finite levels for the markov channel this paper proposes a practical successive decoding scheme with finite levels for the finite state markov channels fsmcs where there is no a priori state information at the transmitter or the receiver the design employs either a random interleaver or a deterministic interleaver with an irregular pattern and an optional iterative estimation and decoding procedure within each level the interleaver design criteria may be the achievable rate or the extrinsic information transfer exit chart depending on the receiver type for random interleavers the optimization problem is solved efficiently using a pilot utility function while for deterministic interleavers a good construction is given using empirical rules simulation results demonstrate that the new successive decoding scheme combined with irregular low density parity check ldpc codes can approach the identically and uniformly distributed i u d input capacity on the markov fading channel using only a few levels

reversible jump markov chain monte carlo computation and bayesian model determination markov chain monte carlo methods for bayesian computation have until recently been restricted to problems where the joint distribution of all variables has a density with respect to some fixed standard underlying measure they have therefore not been available for application to bayesian model determination where the dimensionality of the parameter vector is typically not fixed this paper proposes a new framework for the construction of reversible markov chain samplers that jump between parameter subspaces of differing dimensionality which is flexible and entirely constructive it should therefore have wide applicability in model determination problems the methodology is illustrated with applications to multiple change point analysis in one and two dimensions and to a bayesian comparison of binomial experiments

optimal design and placement of pilot symbols for channel estimation the problem of designing and placing pilot symbols for the estimation of frequency selective random channels is considered the channel is assumed to be a block fading model with finite impulse response fir for both single input single output siso and multiple input multiple output mimo channels under the assumption of independent and identical distributed channel taps the cramer rao bound crb on the mean square error mse of semi blind channel estimators is derived and minimized with respect to pilot symbols and their placement it is shown that the optimal strategy is to place pilot symbols satisfying certain orthogonality condition in such a way that data and pilot symbols with higher power are in the middle of the packet the results also indicate that the optimal pilot placements are independent of channel probability distribution for constant modulus symbols we show that the quasi periodic placement and its generalization in the multiuser case turn out to be optimal we further consider estimating channels with correlated taps and show that the previous placement strategy is also optimal among orthogonal pilot sequences

optimal placement of training for frequency selective block fading channels the problem of placing training symbols optimally for orthogonal frequency division multiplexing ofdm and single carrier systems is considered the channel is assumed to be quasi static with a finite impulse response of length l 1 samples under the assumptions that neither the transmitter nor the receiver knows the channel and that the receiver forms a minimum mean square error mmse channel estimate based on training symbols only training is optimized by maximizing a tight lower bound on the ergodic training based independent and identically distributed i i d capacity for ofdm systems it is shown that the lower bound is maximized by placing the known symbols periodically in frequency for single carrier systems under the assumption that the training symbols are placed in clusters of length spl alpha spl ges 2l 1 it is shown that the lower bound is maximized by a family of placement schemes called qpp spl alpha where qpp stands for quasi periodic placement these placement schemes are formed by grouping the known symbols into as many clusters as possible and then placing these clusters periodically in the packet for both ofdm and single carrier systems the optimum energy tradeoff between training and data is also obtained

full rank and rank deficient precoding schemes for single carrier block transmissions in block mode transmission inserting a cyclic prefix cp between two consecutive blocks provides an efficient way of removing interblock interference and simplifies equalization of frequency selective channels at the receiver here we address optimal training design for channel estimation in such systems our investigations focus on affine precoding schemes in designing the precoder least squares channel estimation is constrained to be decoupled from symbol detection which results in orthogonal precoding schemes if the precoding matrix is full rank the data rate or bandwidth has to be traded off to accommodate training we propose a full rank orthogonal single carrier frosc precoding with a low peak to average power ratio then in order to improve bandwidth efficiency we propose a rank deficient orthogonal single carrier drosc precoding scheme symbol recovery is still possible thanks to the finite alphabet property of the data symbols

on the effect of receiver estimation error upon channel mutual information our goal in this paper is to study the effect of the receiver structure upon the achievable data rates we consider transmission of linearly precoded data symbols over a frequency selective block fading multiple input multiple output mimo wireless channel to encompass a number of transmission schemes we study this problem utilizing affine precoding which is a unified model of linearly precoded data symbols with superimposed training we focus on bayesian receivers that estimate both the unknown fading coefficients and the data symbols the receiver may adopt either of the following strategies to retrieve the data symbols strategy i the receiver obtains joint bayesian channel and symbol estimates strategy ii the receiver obtains a bayesian channel estimate initially and the channel measurement is utilized to estimate the data symbols for both strategies we provide lower bounds on the mutual information between the data symbols and their corresponding estimates and we relate these bounds to the symbol cramer rao bound crb matrices in contrast to strategy ii for strategy i the lower bound does not depend on either the channel estimate or the covariance of the channel estimation error for strategy ii we show that asymptotically as the size of the transmission block grows there is no loss of information after the maximum a posteriori map estimate of gaussian symbols we also provide guidelines to design affine precoders that maximize the derived lower bounds under the total average transmit power constraint

on the sensitivity of a suboptimal precoding scheme for frequency selective block based channels with respect to channel inaccuracies water filling is the precoding scheme that achieves capacity in gaussian parallel or block based channels a suboptimal precoding scheme which has been observed to perform quite close to water filling in some cases of great interest is when all active eigenvectors of the input data covariance matrix receive the same power both techniques require perfect channel knowledge at the transmitter in this work we consider the sensitivity of the suboptimal scheme when a channel estimate is used at the transmitter as if it were the true channel using tools from matrix perturbation theory we derive closed form expressions and bounds relating the channel estimation error covariance matrix with the mean mutual information decrease we thus uncover the factors that determine the behavior of the suboptimal precoding scheme under channel uncertainties simulations are in agreement with our theoretical results

a regularized xfem framework for embedded cohesive interfaces this work focuses on xfem modeling of elastodamaging interfaces characterized by regularized kinematics after regularization of the displacement discontinuity a process zone of finite width with continuous strain fields emerges the stress fields are independently energy deduced modeled via specific constitutive laws and subsequently introduced within the virtual work principle the methodology can address cohesive interfaces with vanishing and finite thickness in a unified way two dimensional results for a strain localization problem and several delamination tests are discussed in detail and compared with previous numerical experimental results