minimum probability of error for asynchronous gaussian multiple access channels consider a gaussian multiple access channel shared by k users who transmit asynchronously independent data streams by modulating a set of assigned signal waveforms the uncoded probability of error achievable by optimum multiuser detectors is investigated it is shown that the k user maximum likelihood sequence detector consists of a bank of single user matched filters followed by a viterbi algorithm whose complexity per binary decision is o 2 k the upper bound analysis of this detector follows an approach based on the decomposition of error sequences the issues of convergence and tightness of the bounds are examined and it is shown that the minimum multiuser error probability is equivalent in the iow noise region to that of a single user system with reduced power these results show that the proposed multiuser detectors afford important performance gains over conventional single user systems in which the signal constellation carries the entire burden of complexity required to achieve a given performance level

optimum asymptotic multiuser efficiency of randomly spread cdma this correspondence analyzes the high signal to noise ratio snr performance of optimum multiuser detectors for synchronous direct sequence spread spectrum with random spreading in an additive white gaussian noise channel under very general conditions on the received powers we show that the optimum asymptotic efficiency of a k user system with spreading gain n converges to 1 almost surely as k spl rarr spl infin and k n is kept equal to an arbitrary nonzero constant therefore the asymptotic behavior of the minimum bit error rate is equivalent to that of a single user system

a chip based multiuser detector for the downlink of a ds cdma system using a folded state transition trellis the maximum likelihood sequence estimation mlse multiuser detector has very good performance but at the expense of high computational complexity the viterbi algorithm is employed to implement the mlse in the asynchronous uplink in this scheme the various bit combinations are taken to be the different states in the decoding trellis however the number of states increases exponentially with the number of active users we propose a scheme that exploits the feature of power equality in the downlink to reduce the number of states involved each transmitted chip value can only take a certain number of possible discrete values using these discrete values as the states in the transition trellis diagram and operating the viterbi algorithm at the chip level the number of states is reduced from 4 sup k to k 1 sup l where k is the number of users and l is the number of paths in the multipath channel

blind multiuser detection from moe to subspace methods the minimum output energy moe multiuser receiver has been shown to approach the minimum mean square error mmse receiver at high signal to noise ratio snr however performance degradation is incurred by noise induced channel estimation error in this paper we propose a power of r por technique to significantly improve the performance of the moe receiver it is shown that the new receiver asymptotically converges to the mmse receiver without performance penalty the convergence is established either under high snr with large exponent raised in the power of the covariance matrix or with sufficiently large number of data samples connection between our por method and a widely studied subspace method is investigated from the respective optimization criteria asymptotic equivalence between these two methods is also established extensive simulations based on finite data samples show that the proposed method significantly outperforms the subspace method in systems with medium to heavy loading severe multipath distortion or smaller processing gain moreover adaptive implementation of the proposed method exhibits very robust performance in a dynamic loading environment

performance of constrained and unconstrained adaptive multiuser detectors for quasi synchronous cdma it has previously been shown that multiuser interference in a quasi synchronous code division multiple access qs cdma system can be effectively rejected using a nonadaptive decorrelator however the qs decorrelator is orthogonal to the inflated subspace spanned by the undesired users with arbitrary delays in the qs uncertainty interval and hence does not perform as well as a decorrelator with a priori knowledge of the delays here we consider a constrained adaptive linear suppression filter which implicitly estimates the delays of the qs undesired signals and thus approaches the ideal decorrelator of lupas and verdu 1990 for qs cdma it is shown through analysis and simulations that the constrained recursive least squares c rls algorithm converges faster than an unconstrained rls adaptive filter and generally outperforms the nonadaptive qs decorrelator a cellular quasi synchronous system is discussed in the present paper

blind parameter estimation in multiple access systems a blind algorithm for the estimation of amplitude phase and relative time delay of each user in multiple access communication systems is proposed this algorithm is based on the cyclostationarity features of the received signals and provides estimates of the unknown parameters that are intrinsically immune to the effects of noise and interference provided that a cycle frequency of the user signals exists which is not shared with the disturbance terms the proposed estimators are under mild assumptions asymptotically unbiased and consistent moreover the proposed algorithm is asymptotically near far resistant and is not based on the usual assumption of white and or gaussian noise

truncated unscented kalman filtering we devise a filtering algorithm to approximate the first two moments of the posterior probability density function pdf the novelties of the algorithm are in the update step if the likelihood has a bounded support we can use a modified prior distribution that meets bayes rule exactly applying a kalman filter kf to the modified prior distribution referred to as truncated kalman filter tkf can vastly improve the performance of the conventional kalman filter particularly when the measurements are informative relative to the prior the application of the tkf to practical problems in which the measurement noise pdf has unbounded support is achieved by imposing several approximating assumptions which are valid only when the measurements are informative this implies that we adaptively choose between an approximation to the kf or the tkf according to the information provided by the measurement the resulting algorithm based on the unscented transformation is referred to as truncated unscented kf

bayesian parameter estimation using periodic cost functions in this paper a new method for bayesian periodic parameter estimation is derived using periodic cost functions the method named parameter estimation via root finding perf is based on fourier series representation of the bayes periodic risk functions the perf method is implemented for minimum cyclic error minimum absolute periodic error and minimum mean square periodic error mspe estimators and the corresponding estimators are derived the periodic estimators are applied to direction of arrival and phase estimation problems and compared with the minimum mean square error and maximum a posteriori probability estimators and the periodic ziv zakai lower bound in terms of mspe

indecomposable error sequences in multiuser detection in this paper we provide a graph based characterization of the set of indecomposable sequences that are useful in the computation of an upper bound to error probability of maximum likelihood ml detection in code division multiple access cdma multiuser systems we apply this characterization to a k user symmetric system and to a two user two rate system it leads to a precise calculation of the bound which is then compared to the performance of a decorrelator

asymptotic multiuser efficiencies for decision directed multiuser detectors the asymptotic multiuser efficiencies ames are derived for various classes of decision directed multiuser detectors including multistage detectors and decision feedback detectors novel classes of soft decision multistage detectors are proposed and analyzed each class is specified in part by a soft decision nonlinearity such as a symmetric quantizer or a linear clipper closed form expressions for two user ames are derived for soft decision two stage detectors and can be used as a design criterion to optimize the soft decision nonlinearities for a special case of two synchronous users the soft decision two stage detector using an optimized linear clipper with either conventional or decorrelated tentative decisions is shown to achieve optimum ame upper and lower bounds on the ame are obtained for decision feedback detectors using either conventional or decorrelated tentative decisions it is demonstrated that decision directed multiuser detectors with conventional tentative decisions have low near far resistance compared to those with decorrelated tentative decisions

error probability for direct sequence spread spectrum multiple access communications part i upper and lower bounds upper and lower bounds on the average probability of error are obtained for direct sequence spread spectrum multipleaccess communications systems with additive white gaussian noise channels the bounds which are developed from convexity properties of the error probability function are valid for systems in which the maximum multiple access interference does not exceed the desired signal and the signature sequence period is equal to the duration of the data pulse the tightness of the bounds is examined for systems with a small number of simultaneously active transmitters this is accomplished by comparisons of the upper and lower bounds for several values of the system parameters the bounds are also compared with an approximation based on the signal to noise ratio and with the chernoff upper bound

limited linear cancellation of multiuser interference in ds cdma asynchronous systems this paper presents a linear cancellation detector for the gaussian channel operating over limited time intervals of the received signal in a similar way to a multiinput multioutput finite impulse response fir filter the parameters defining the detector become time invariant and the conditions to be met by the signatures are stated a bound for the multiuser interference due to the limited time correlation and upper and lower bounds for the error probability are obtained the theoretical bounds and numerical results show that the detector is adequate for systems intended for many users whose amplitudes can be restricted to a given range

suboptimum multiuser receivers for convolutionally coded asynchronous ds cdma systems motivated by the high complexity of the optimal sequence estimator for convolutionally coded asynchronous code division multiple access cdma systems developed by giallorenzi and wilson see ibid vol 44 no 8 p 997 1996 and the potentially poor performance of the conventional receiver due to multiuser interference and the near far problem we examine relatively simple multiuser receivers which perform nearly as well as the optimal receiver the multiuser receivers discussed are of two types the first set of approaches are partitioned approaches that treat the multiuser interference equalization problem and the decoding problem separately the second set of approaches are integrated approaches that perform both the equalization and decoding operations together we study linear decision feedback and trellis tree based approaches in each category the asymptotic efficiency of this receiver relative to an uncoded coherent binary phase shift keying bpsk receiver termed asymptotic multiuser coding gain or amcg is used as a performance criterion throughout also computer simulations are used whenever the computation of the amcg is not feasible it is shown that a number of the approaches which are introduced achieve a high performance level with a moderate complexity

the statistical performance of some instantaneous frequency estimators the authors examine the class of smoothed central finite difference scfd instantaneous frequency if estimators which are based on finite differencing of the phase of the analytic signal these estimators are closely related to if estimation via the periodic first moment with respect to frequency of discrete time frequency representations tfrs in l cohen s 1966 class the authors determine the distribution of this class of estimators and establish a framework which allows the comparison of several other estimators such as the zero crossing estimator and one based on linear regression on the signal phase it is found that the regression if estimator is biased and exhibits a large threshold for much of the frequency range by replacing the linear convolution operation in the regression estimator with the appropriate convolution operation for circular data the authors obtain the parabolic scfd pscfd estimator which is unbiased and has a frequency independent variance yet retains the optimal performance and simplicity of the original estimator

subspace based channel estimation for code division multiple access communication systems we consider the estimation of channel parameters for code division multiple access cdma communication systems operating over channels with either single or multiple propagation paths the multiuser channel estimation problem is decomposed into a series of single user problems through a subspace based approach by exploiting the eigenstructure of the received signal s sample correlation matrix the observation space can be partitioned into a signal subspace and a noise subspace without prior knowledge of the unknown parameters the channel estimate is formed by projecting a given user s spreading waveform into the estimated noise subspace and then either minimizing the likelihood or minimizing the euclidean norm of this projection both of these approaches yield algorithms which are near far resistant and do not require a preamble

group detection for synchronous gaussian code division multiple access channels the concept of group detection is introduced to address the design of suboptimum multiuser detectors for code division multiple access cdma channels a group detection scheme consists of a bank of p group detectors one each for detecting the information symbols of users in each group of a p group partition of the k simultaneously transmitting users in a parallel group detection scheme these group detectors operate independently whereas in a sequential scheme each group detector uses the decisions of the previous group detectors to successively cancel the interference from those users group detectors based on the generalized likelihood ratio test glrt are obtained for the synchronous gaussian cdma channel the complexity of these detectors is exponential in the group size whereas that of the optimum detector is exponential in k since the partition of users is a design parameter group sizes can be chosen to satisfy a wide range of complexity constraints a key performance result is that the glrt group detectors are optimally group near far resistant furthermore upper and lower bounds on the asymptotic efficiency of the sequential group detectors are derived these bounds reveal that the sequential group detectors can under certain conditions perform as well as glrt group detectors of much larger group sizes group detection provides a unifying approach to multiuser detection when the users are partitioned into k single user groups the glrt a modified form of glrt and the sequential group detectors reduce to previously proposed suboptimal detectors namely the decorrelator the two stage detector and the decorrelating decision feedback detector respectively for the other nontrivial partitions the group detectors are new and have a performance that is commensurate with their complexity

indirectly estimated adaptive detectors for code division multiple access signals this paper presents the development of indirectly estimated adaptive idea detectors for code division multiple access cdma signals in wireless communication systems multiuser cdma detection is formulated as an inverse problem in the presence of noise and the estimation of the detector parameters is accomplished using elements of regularization theory the development of autonomous cdma detectors that are capable of adjusting to the channel characteristics with the support of training sequences relies on data dependent procedures designed to reduce the effect of noise and interfering users on the performance of the detector the detector parameters can be computed by adaptive algorithms that require no matrix inversion the proposed idea detector is evaluated and compared with existing multiuser cdma detectors in terms of their robustness to noise resistance to the near far problem and ability to handle multipath signals

robust blind multiuser detection based on the worst case performance optimization of the mmse receiver the conventional minimum mean square error mmse multiuser receiver requires that each particular user transmits a sequence of training symbols known to the receiver and the receiver estimates the user signatures using this knowledge however in the presence of multiaccess interference mai during the training period and or in scenarios with short training sequence length the signature estimates can be erroneous and the performance of the mmse multiuser receiver can degrade substantially in this paper we propose a new blind multiuser receiver that is robust against the effects of erroneously presumed desired user signature and short data length our approach is based on the explicit modeling of possible mismatches in the mean square error cost function and worst case performance optimization we show that this approach leads to a multiuser receiver which uses the data covariance matrix with an adaptive diagonal loading the proposed method has simple implementation with a computational complexity comparable with that of the fixed diagonal loading based multiuser receiver simulation results show performance improvements achieved by our approach relative to existing techniques

on minimal eigenvalues of a class of tridiagonal matrices it is known that the worst case near far resistance of optimum multiuser detectors for asynchronous gaussian multiple access channels can be expressed in terms of a class of block tridiagonal matrices and the minimal eigenvalues of such a class of block tridiagonal matrices serve as a good measure of the worst case near far resistance in this paper we focus on the two user scenario where each block tridiagonal matrix under consideration is a tridiagonal matrix we derive closed form expressions for the minimal eigenvalues of such a class of tridiagonal matrices in terms of the largest real solution of a trigonometric equation in 0 pi we also obtain lower bounds and upper bounds on the minimal eigenvalues which improve on previously known results in the literature

using angular dispersion of gradient direction for detecting edge ribbons edges in a scene generally project to smooth continuous curves nearly everywhere in the image which results in low angular deviation of the intensity gradients in small neighborhoods straddling edges angular deviation is shown to be a measure of snr a theoretical analysis of angular deviation arising due to independent and identically distributed n 0 sigma sup 2 random noise is presented angular deviation thresholds for neighborhood sizes from 3 3 to 11 11 pixels are determined both from this analysis and numerical examples the proposed gradient angular dispersion detection algorithm detects edge elements by comparing the measured angular deviation with values computed for the minimum acceptable snr low values of deviation violate the no edge hypothesis the algorithm is shown to make good use of the limited dynamic range of the imaging system the sensitivity and selectivity of the strategy are both shown to be high

multiuser detection in single path fading channels the performance analysis of maximum likelihood sequence and decorrelating multiuser detectors is developed for the single path rayleigh fading channel the received signal in this multipoint to point channel is additively composed of white gaussian noise and independently faded waveforms from a finite number of asynchronous users the optimum sequence detector consists of a bank of single user matched filters followed by a dynamic programming algorithm has a demodulation complexity per symbol which is exponential in the number of users and requires the knowledge of the system as well of the fading parameters the decorrelating detector has a complexity which is polynomial in the number of users and does not require knowledge of the signal amplitudes which are assumed to vary slowly relative to the symbol rate the single user error rates are presented for both detectors and compared to conventional detection and isolated transmission and the notion of asymptotic multiuser efficiency is developed for this channel in contrast to conventional detection which suffers from near far effects due to rayleigh fading it is shown that the aforementioned multiuser detectors exhibit performance which rivals that of isolated transmission for sufficiently small thermal noise power the results of the analysis are illustrated with numerical examples and indicate that the near far problem may be alleviated by a more sophisticated receiver design

gradient estimation for sensitivity analysis and adaptive multiuser interference rejection in code division multiple access systems in this paper we consider a direct sequence code division multiple access ds cdma system in the framework of a discrete event dynamic system deds in order to optimize the system performance based on this formulation we develop infinitesimal perturbation analysis ipa for estimating the sensitivity of the average probability of bit error to factors ranging from near far effects to imperfections in power control the above estimates are shown to be unbiased and this technique is then further incorporated into a stochastic gradient algorithm for achieving adaptive multiuser interference rejection for such systems which is also subject to frequency nonselective slow fading we use an ipa based stochastic training algorithm for developing an adaptive linear detector with the average probability of error being the minimization criterion we also develop a practical implementation of such an adaptive detector where we use a joint estimation detection algorithm for minimizing the average probability of bit error a sequential implementation that does not require a stochastic training sequence or a preamble is also developed

a note on a classical bound for the moduli of all zeros of a polynomial considers the monic polynomial f z z sup n a sub n 1 z sup n 1 a sub 0 in the complex variable z with complex coefficients under the assumption that the nonleading coefficients of f lie in the disk mod z mod

cyclic barankin type bounds for non bayesian periodic parameter estimation in many practical periodic parameter estimation problems the appropriate performance criteria are periodic in the parameter space the existing mean square error mse lower bounds such as cramer rao bound crb and barankin type bounds do not provide valid lower bounds in such problems in this paper cyclic versions of the crb and the barankin type bounds hammersley chapman robbins and mcaulay seidman are derived for non bayesian parameter estimation the proposed bounds are lower bounds on the mean cyclic error mce of any cyclic unbiased estimator where the cyclic unbiasedness is defined by using lehmann unbiasedness these mce lower bounds can be readily obtained from existing mse lower bounds and thus can be easily calculated the cyclic barankin type bounds and the performance of the maximum likelihood ml estimator are compared in terms of mce in von mises distributed measurements problem and for frequency and amplitude estimation with gaussian noise in these problems the ml estimator is found to be cyclic unbiased

on the capacity loss due to separation of detection and decoding the performance loss due to separation of detection and decoding on the binary input additive white gaussian noise awgn channel is quantified in terms of mutual information results are reported for both the code division multiple access cdma channel in the large system limit and the intersymbol interference isi channel the results for cdma rely on the replica method developed in statistical mechanics it is shown that a previous result of shamai and verdu found for gaussian input alphabet holds also for binary input alphabets for the isi channel the performance loss is calculated via the bahl cocke jelinek raviv bcjr algorithm comparisons are made to the capacity of separate detection and decoding using suboptimum detectors such as a decision feedback equalizer

new result for the annular bounds of complex coefficient polynomial zeros in this note we provide the annular bound for the zeros of complex coefficient polynomial such an annular bound can be easily obtained by estimating the largest nonnegative zeros of specific four polynomials two examples are also provided to show that the proposed annular bound is less conservative than the existing results reported recently

error probability for direct sequence spread spectrum multiple access communications part ii approximations approximations are obtained for the average probability of error in an asynchronous direct sequence spread spectrum multiple access communications system both binary and quaternary systems are considered and the chip waveforms are allowed to be arbitrary time limited waveforms with time duration equal to the inverse of the chip rate the approximation is based on the integration of the characteristic function of the multiple access interference the amount of computation required to evaluate this approximation grows only linearly with the product of the number of simultaneous transmitters and the number of chips per bit the accuracy of the approximation is extremely good in most cases but it can be improved if necessary by an application of a series expansion numerical results are presented for specific chip waveforms and signature sequences

linear multiuser detectors for synchronous code division multiple access channels under the assumptions of symbol synchronous transmissions and white gaussian noise the authors analyze the detection mechanism at the receiver comparing different detectors by their bit error rates in the low background noise region and by their worst case behavior in a near far environment where the received energies of the users are not necessarily similar optimum multiuser detection achieves important performance gains over conventional single user detection at the expense of computational complexity that grows exponentially with the number of users it is shown that in the synchronous case the performance achieved by linear multiuser detectors is similar to that of optimum multiuser detection attention is focused on detectors whose linear memoryless transformation is a generalized inverse of the matrix of signature waveform crosscorrelations and on the optimum linear detector it is shown that the generalized inverse detectors exhibit the same degree of near far resistance as the optimum multiuser detectors the optimum linear detector is obtained

reduced dimension multiuser detection we present a reduced dimension multiuser detector rd mud structure for synchronous systems that significantly decreases the number of required correlation branches at the receiver front end while still achieving performance similar to that of the conventional matched filter mf bank rd mud exploits the fact that in some wireless systems the number of active users may be small relative to the total number of users in the system hence the ideas of analog compressed sensing may be used to reduce the number of correlators the correlating signals used by each correlator are chosen as an appropriate linear combination of the users spreading waveforms we derive the probability of symbol error when using two methods for recovery of active users and their transmitted symbols the reduced dimension decorrelating rdd detector which combines subspace projection and thresholding to determine active users and sign detection for data recovery and the reduced dimension decision feedback rddf detector which combines decision feedback matching pursuit for active user detection and sign detection for data recovery we derive probability of error bounds for both detectors and show that the number of correlators needed to achieve a small probability of symbol error is on the order of the logarithm of the number of users in the system the theoretical performance results are validated via numerical simulations

a generalized minimum mean output energy strategy for cdma systems with improper mai it has been shown that in a direct sequence code division multiple access ds cdma system employing binary phase shift keying bpsk modulation the baseband equivalent of the cdma multiplex is under very mild assumptions an improper complex random process i e it has a nonzero pseudoautocorrelation function the problem of linear multiuser detection for asynchronous ds cdma systems with improper multiaccess interference mai is considered a new mean output energy moe cost function is introduced whose constrained minimization leads to two new linear multiuser detectors exploiting the information contained in the pseudoautocorrelation of the observables and which generalize the classical decorrelating and minimum mean square error mmse receivers the problem of blind adaptive receiver implementation based on subspace tracking is also tackled finally the superiority of the new detectors with respect to the classical linear detection structures present in the literature is demonstrated through both theoretical considerations and computer simulations

a near optimal multiuser detector for ds cdma systems using semidefinite programming relaxation a multiuser detector for direct sequence code division multiple access systems based on semidefinite programming sdp is proposed it is shown that maximum likelihood ml detection can be carried out by relaxing the associated integer programming problem to a dual sdp problem which leads to a detector of polynomial complexity computer simulations that demonstrate that the proposed detector offers near optimal performance with considerably reduced computational complexity compared with that of existing primal sdp relaxation based detectors are presented

fast median filtering for phase or orientation data median filtering is among the most utilized tools for smoothing real valued data as it is robust edge preserving value preserving and yet can be computed efficiently for data living on the unit circle such as phase data or orientation data a filter with similar properties is desirable for these data there is no unique means to define a median so we discuss various possibilities the arc distance median turns out to be the only variant which leads to robust edge preserving and value preserving smoothing however there are no efficient algorithms for filtering based on the arc distance median here we propose fast algorithms for filtering of signals and images with values on the unit circle based on the arc distance median for non quantized data we develop an algorithm that scales linearly with the filter size the runtime of our reference implementation is only moderately higher than the matlab implementation of the classical median filter for real valued data for quantized data we obtain an algorithm of constant complexity w r t the filter size we demonstrate the performance of our algorithms for real life data sets phase images from interferometric synthetic aperture radar planar flow fields from optical flow and time series of wind directions

randomly spread cdma asymptotics via statistical physics this paper studies randomly spread code division multiple access cdma and multiuser detection in the large system limit using the replica method developed in statistical physics arbitrary input distributions and flat fading are considered a generic multiuser detector in the form of the posterior mean estimator is applied before single user decoding the generic detector can be particularized to the matched filter decorrelator linear minimum mean square error mmse detector the jointly or the individually optimal detector and others it is found that the detection output for each user although in general asymptotically non gaussian conditioned on the transmitted symbol converges as the number of users go to infinity to a deterministic function of a hidden gaussian statistic independent of the interferers thus the multiuser channel can be decoupled each user experiences an equivalent single user gaussian channel whose signal to noise ratio snr suffers a degradation due to the multiple access interference mai the uncoded error performance e g symbol error rate and the mutual information can then be fully characterized using the degradation factor also known as the multiuser efficiency which can be obtained by solving a pair of coupled fixed point equations identified in this paper based on a general linear vector channel model the results are also applicable to multiple input multiple output mimo channels such as in multiantenna systems

lattice decoding for joint detection in direct sequence cdma systems a new joint detection method based on sphere packing lattice decoding is presented in this paper the algorithm is suitable for both synchronous and asynchronous multiple access direct sequence code division multiple access ds cdma systems and it may jointly detect up to 64 users with a reasonable complexity the detection complexity is independent of the modulation size and large m pam or m qam constellations can be used furthermore a theoretical gain analysis is performed in which the multiple access system performance is derived from the lattice parameters

on the infinite families of zero bounds of complex polynomials we derive several classes of zero bounds for univariate polynomials with complex coefficients the derivations are based on the iterative algorithms of graffe and jin and the approximation methods of newton and kalantari all of the proposed bounds are shown to be asymptotically sharp and the convergence speeds are compared in particular we derive an improving factor to tighten kalantari s bounds this factor and kalantari s bound can both be readily computed with a precalculated lookup table we also propose a modified version of kalantari s bound that is independent of the table and we prove that under some conditions our bound is tighter numerical examples are provided to illustrate the effectiveness of our results

low complexity blind detection of ds cdma signals auxiliary vector receivers a fresh look on the design of practical low complexity direct sequence code division multiple access ds cdma receivers is proposed from the wiener reconstruction filter point of view the natural outcome is the emergence of a new class of linear scalar parameterized auxiliary vector receivers filters then the blind optimization of these receivers in the maximum signal to interference plus noise ratio sinr sense becomes a straightforward procedure the conceptual and computational simplicity of this general approach promises immediate practical utility this new generation of receivers exhibits minimal optimization requirements and near matched filter mf operational complexity yet theoretical arguments supported by numerical and simulation results included in this work suggest that the blind auxiliary vector receiver compares favorably both complexity wise and performance wise to multiuser mu detectors such as the minimum output energy moe and the decorrelating receiver although the latter utilizes the assumed known spreading codes of all interfering users

nonlinear processing and analysis of angular signals physical quantities referring to angles like vector direction color hue etc exhibit an inherently periodic nature due to this periodicity digital filters and edge operators proposed for data on the line cannot be applied on such data we introduce filters for angular signals circular mean circular median circular a trimmed mean circular modified trimmed mean particular emphasis is given to the circular median filter for which some interesting properties are derived we also use estimators of circular dispersion to introduce edge detectors for angular signals three variations for the extension of quasirange to circular data are proposed and expressions for their output pdf are derived these circular quasiranges have good and user controlled properties as edge detectors in noisy angular signals the performance of the proposed edge operators is evaluated on angular edges using certain quantitative criteria finally a series of experiments featuring one dimensional 1 d angular signals and hue images is used to illustrate the operation of the new filters and edge detectors

toward color image segmentation in analog vlsi algorithm and hardware standard techniques for segmenting color images are based on finding normalized rgb discontinuities color histogramming or clustering techniques in rgb or cie color spaces the use of the psychophysical variable hue in hsi space has not been popular due to its numerical instability at low saturations in this article we propose the use of a simplified hue description suitable for implementation in analog vlsi we demonstrate that if theintegrated white condition holds hue is invariant to certain types of highlights shading and shadows this is due to theadditive shift invariance property a property that other color variables lack the more restrictive uniformly varying lighting model associated with themultiplicative scale invariance property shared by both hue and normalized rgb allows invariance to transparencies and to simple models of shading and shadows using binary hue discontinuities in conjunction with first order type of surface interpolation we demonstrate these invariant properties and compare them against the performance of rgb normalized rgb and cie color spaces we argue that working in hsi space offers an effective method for segmenting scenes in the presence of confounding cues due to shading transparency highlights and shadows based on this work we designed and fabricated for the first time an analog cmos vlsi circuit with on board phototransistor input that computes normalized color and hue

differentially coherent decorrelating detector for cdma single path time varying rayleigh fading channels this paper describes a differentially coherent decorrelating detector for a k user reverse link code division multiple access environment that exhibits time varying rayleigh fading the channel is modeled as providing only a single fading path for each user and with no additional means to achieve diversity the design of the detector is based on using fractionally sampled matched filter outputs to simultaneously achieve two goals 1 the novel realization of a one shot decorrelator with lower computational complexity and 2 the forming of the maximum likelihood decision rule on the decorrelated outputs which results in an effective increase of the correlation in the fading process analytical evaluation and simulation of the error probability of the detector demonstrates significant lowering of the error floor in comparison to the decorrelating detector that employs conventional differentially coherent detection

on the average near far resistance for mmse detection of direct sequence cdma signals with random spreading the performance of a near far resistant finite complexity minimum mean squared error mmse linear detector for demodulating direct sequence ds code division multiple access cdma signals is studied assuming that the users are assigned random signature sequences we obtain tight upper and lower bounds on the expected near far resistance of the mmse detector averaged over signature sequences and delays as a function of the processing gain and the number of users since the mmse detector is optimally near far resistant these bounds apply to any multiuser detector that uses the same observation interval and sampling rate the lower bound on near far resistance implies that even without power control linear multiuser detection provides near far resistant performance for a number of users that grows linearly with the processing gain

time varying narrow band interference rejection in asynchronous multiuser ds cdma systems over frequency selective fading channels in this paper we handle the problem of joint suppression of multiple access interference mai and narrowband interference nbi in fading dispersive channels the detectors we consider are linear one shot structures which allow for possible window enlargement and signal space oversampling to improve performance we focus on both zero forcing and minimum mean square error design strategies showing that the presence of nbi generally requires a time varying processing of the observables no matter what the optimization criterion a thorough performance assessment of the proposed detectors is also presented either through analytical formulas or through computer simulations we finally deal with the problem of blind suppression of both mai and nbi introducing batch estimation procedures to be implemented offline which require very little and sometimes no prior knowledge as to the interference structure

on adaptive minimum probability of error linear filter receivers for ds cdma channels receiver architectures in the form of a linear filter front end followed by a hard limiting decision maker are considered for ds cdma communication systems based on stochastic approximation concepts a recursive algorithm is developed for the adaptive optimization of the linear filter front end in the minimum ber sense the recursive form is decision driven and distribution free for additive white gaussian noise awgn channels theoretical analysis of the ber surface of linear filter receivers identifies the subset of the linear filter space where the optimal receiver lies and offers a formal proof of guaranteed global optimization with probability one for the two user case to the extent that the output of a linear ds cdma filter can be approximated by a gaussian random variable a minimum mean square error optimized linear filter approximates the minimum ber solution numerical and simulation results indicate that for realistic awgn ds cdma systems with reasonably low signature cross correlations the linear minimum ber filter and the mmse filter exhibit approximately the same performance the linear minimum ber receiver is superior however when either the signature cross correlation is high or the background noise is non gaussian

em based joint data detection and channel estimation of ds cdma signals we present two efficient iterative receiver structures of tractable complexity for joint multiuser detection and multichannel estimation jde of direct sequence code division multiple access signals the schemes result from an application of the expectation maximization em and the space alternating generalized expectation maximization sage algorithms respectively the em jde receiver updates the data bit sequences in parallel while the sage jde receiver reestimates them successively the channel parameters are updated in parallel in both schemes the em algorithm provides a set of free parameters called weight coefficients which can be selected to optimize its performance two optimality criteria are defined and analytical expressions for the corresponding optimized weight coefficients are given monte carlo simulations of a synchronous scenario show that the proposed jde receivers have excellent multiuser efficiency and are robust against errors in the estimation of the channel parameters moreover very short training sequences are required for the jde schemes to converge simulation results further demonstrate that the sage jde receiver exhibits a better performance when the users bit sequences are updated in the order of increasing signal strength i e the bit sequence of the user with the weakest signal strength is updated first at each stage

a frequency domain multi user detector for td cdma systems in this paper a novel frequency domain multi user detector is proposed for a time division code division multiple access td cdma up link unlike conventional frequency domain detectors the proposed detector first transforms the system matrix of td cdma systems into a circulant matrix by cyclic truncation it subsequently uses a new method to convert the circulant matrix into a frequency domain block diagonalized matrix through discrete fourier transforms and permutations therefore the proposed detector can utilize the channel frequency domain coherence to further decrease its computational complexity with a controlled performance loss moreover a novel approach is proposed to calculate the frequency domain correlation matrix and matched filter with the help of this novel approach the proposed detector expresses significant complexity advantage over other frequency domain detectors for a real td cdma system in a short time dispersive channel

cdna microarray image processing using fuzzy vector filtering framework this paper presents a novel filtering framework capable of processing cdna microarray images the proposed two component adaptive vector filters integrate well known concepts from the areas of fuzzy set theory nonlinear filtering multidimensional scaling and robust order statistics by appropriately setting the weighting coefficients in a generalized framework the method is capable of removing noise impairments while preserving structural information in cdna microarray images noise removal is performed by tuning a membership function which utilizes distance criteria applied to cdna vectorial inputs at each image location the classical vector representation adopted here for a two channel processing task as well as a new color ratio model representation are used simulation studies reported in this paper indicate that the proposed adaptive fuzzy vector filters are computationally attractive yield excellent performance and are able to preserve structural information while efficiently suppressing noise in cdna microarray data