dynamics of a predator prey model we describe the bifurcation diagram of limit cycles that appear in the first realistic quadrant of the predator prey model proposed by r m may stability and complexity in model ecosystems princeton university press princeton nj 1974 in particular we give a qualitative description of the bifurcation curve when two limit cycles collapse on a semistable limit cycle and disappear moreover we show that locally asymptotic stability of a positive equilibrium point does not imply global stability for this class of predator prey models

noncoherent ostbc ofdm for mimo and cooperative communications perfect channel identifiability and achievable diversity order this paper considers the context of orthogonal space time block coded ofdm ostbc ofdm without channel state information at the receiver assuming noncoherent maximum likelihood detection the interest herein lies in detection within one ostbc ofdm block motivated by its capability of accommodating relatively fast block fading channels our investigation focuses on analysis aspects where we seek to establish practical noncoherent bpsk qpsk ostbc ofdm schemes that have provably good channel identifiability and diversity properties we consider perfect channel identifiability pci a strong condition guaranteeing unique noncoherent channel identification for any nonzero channel through a judicious design involving special ostbcs and pilot placement we propose an ostbc ofdm scheme that is pci achieving and consumes fewer pilots compared to conventional pilot aided channel estimation methods we further our analysis by showing that a pci achieving scheme also achieves maximal noncoherent spatial diversity for the kronecker gaussian spatial temporal channel fading model which covers the popular i i d rayleigh fading channel and a variety of correlated and sparse multipath channels all these results are developed in parallel for the centralized point to point mimo scenario and a distributed relay communication scenario for the latter scenario our diversity analysis shows that the pci achieving scheme can also achieve maximal noncoherent cooperative diversity the performance merits of the proposed pci achieving scheme are demonstrated by simulations

asymptotic bep and sep of quadratic diversity combining receivers in correlated ricean fading non gaussian noise and interference in this paper we study the asymptotic behavior of the bit error probability bep and the symbol error probability sep of quadratic diversity combining schemes such as coherent maximum ratio combining mrc differential equal gain combining egc and noncoherent combining nc in correlated ricean fading and non gaussian noise which in our definition also includes interference we provide simple and easy to evaluate asymptotic bep and sep expressions which show that at high signal to noise ratios snrs the performance of the considered combining schemes depends on certain moments of the noise and interference impairing the transmission we derive general rules for calculation of these moments and we provide closed form expressions for the moments of several practically important types of noise such as spatially dependent and spatially independent gaussian mixture noise correlated synchronous and asynchronous co channel interference and correlated gaussian interference from our asymptotic results we conclude that a the asymptotic performance loss of binary frequency shift keying bfsk with nc compared to binary phase shift keying bpsk with mrc is always 6 db independent of the type of noise and the number of diversity branches b the asymptotic performance loss of differential egc compared to mrc is always 3 db for additive white gaussian noise but depends on the number of diversity branches and may be larger or smaller than 3 db for other types of noise and c not only fading correlation but also noise correlation negatively affects the performance of quadratic diversity combiners

limiting performance of block fading channels with multiple antennas we derive the performance limits of a radio system consisting of a transmitter with t antennas and a receiver with r antennas a block fading channel with additive white gaussian noise awgn delay and transmit power constraints and perfect channel state information available at both the transmitter and the receiver because of a delay constraint the transmission of a codeword is assumed to span a finite and typically small number m of independent channel realizations therefore the relevant performance limits are the information outage probability and the delay limited or nonergodic capacity we derive the coding scheme that minimizes the information outage probability this scheme can be interpreted as the concatenation of an optimal code for the awgn channel without fading to an optimal beamformer for this optimal scheme we evaluate minimum outage probability and delay limited capacity among other results we prove that for the fairly general class of regular fading channels the asymptotic delay limited capacity slope expressed in bits per second per hertz b s hz per decibel of transmit signal to noise ratio snr is proportional to min t r and independent of the number of fading blocks m since m is a measure of the time diversity induced by interleaving or of the frequency diversity of the system this result shows that if channel state information is available also to the transmitter very high rates with asymptotically small error probabilities are achievable without the need of deep interleaving or high frequency diversity moreover for a large number of antennas delay limited capacity approaches ergodic capacity

approximation of achievable rates in additive gaussian mixture noise channels in this paper we detail effective methods to approximate the achievable rates of channels with additive gaussian mixture gm noise for both real and complex channels to achieve any desired level of accuracy attention is paid to a gaussian input a discrete real input and a complex input with discrete amplitude and independent uniform phase such discrete inputs represent a wide range of input distributions and they include the capacity achieving inputs as special cases at first we propose a simple technique to accurately calculate the noise entropy specifically when the noise level is high a lower bound on the integrand of the entropy is established and the noise entropy can be estimated using a closed form solution in the low noise region the piecewise linear curve fitting pwlcf method is applied we then extend this result to calculate the achievable rate when the input is gaussian distributed which is shown to be asymptotically optimal next we propose a simple pwlcf based method to approximate the output entropy for a real gm channel when the input is discrete and for a complex gm channel when the input is discrete in amplitude with independent uniform phase in particular for the real channel the output entropy is evaluated by examining the output in high and low regions of amplitude using a lower bound on the integrand of the output entropy and pwlcf respectively for the complex channel the output entropy is approximated a similar manner but using polar coordinates and the kernel function it is demonstrated that the output entropy and consequently the achievable rates can be computed to achieve any given accuracy level

log concavity property of the error probability with application to local bounds for wireless communications a clear understanding of the behavior of error probability ep as a function of signal to noise ratio snr and other system parameters is fundamental for assessing the design of digital wireless communication systems we propose an analytical framework based on the log concavity property of the ep which we prove for a wide family of multidimensional modulation formats in the presence of gaussian disturbances and fading based on this property we construct a class of local bounds for the ep that improve known generic bounds in a given region of the snr and are invertible as well as easily tractable for further analysis this concept is motivated by the fact that communication systems often operate with performance in a certain region of interest roi and thus it may be advantageous to have tighter bounds within this region instead of generic bounds valid for all snrs we present a possible application of these local bounds but their relevance is beyond the example made in this paper

on the design of space time and space frequency codes for mimo frequency selective fading channels the authors introduced an algebraic design framework for space time coding in flat fading channels we extend this framework to design algebraic codes for multiple input multiple output mimo frequency selective fading channels the proposed codes strive to optimally exploit both the spatial and frequency diversity available in the channel we consider two design approaches the first uses space time coding and maximum likelihood decoding to exploit the multi path nature of the channel at the expense of increased receiver complexity within this time domain framework we also propose a serially concatenated coding construction which is shown to offer a performance gain with a reasonable complexity iterative receiver in some scenarios the second approach utilizes the orthogonal frequency division multiplexing technique to transform the mimo multipath channel into a mimo flat block fading channel the algebraic framework is then used to construct space frequency codes sfc that optimally exploit the diversity available in the resulting flat block fading channel finally the two approaches are compared in terms of decoder complexity maximum achievable diversity advantage and simulated frame error rate performance in certain representative scenarios

new analytical probability of error expressions for classes of orthogonal signals in rayleigh fading new exact expressions for the symbol error rate and bit error rate of coherent 3 ary and 4 ary orthogonal and transorthogonal signaling in slowly fading rayleigh channels are derived new exact error probability expressions for coherent 6 ary and 8 ary biorthogonal signaling in slow rayleigh fading are also presented the use of these exact expressions as accurate approximations for the error rates of m ary orthogonal biorthogonal and transorthogonal signaling with arbitrary m is illustrated

performance analysis and design criteria of bicm id with signal space diversity for keyhole nakagami m fading channels this paper generalizes the application bit interleaved coded modulation with iterative decoding bicm id using signal space diversity ssd over keyhole nakagami m fading channels the tight union bound on the asymptotic error performance is first analytically derived the near optimal rotation matrix with respect to both the asymptotic performance and the convergence behavior is then determined in particular it is demonstrated that the suitable rotation matrix is the one that has 1 all entries equal in magnitude 2 a high diversity order and 3 a large minimum product of the ratios between squared distances to the power m and log squared distances to the power m of the rotated constellation scaled by factors of signal to noise ratio snr and the parameter m various analytical and simulation results show that by employing ssd with a sufficiently large dimension the error performance can closely approach that over an additive white gaussian noise awgn channel even in the worst case of keyhole fading

recent advances of stretched gaussian distribution underlying hausdorff fractal distance and its applications in fitting stretched gaussian noise abstract this paper summarizes the latest advances of the third author s research group on stretched gaussian distribution underlying the hausdorff fractal theory and its applications in fitting stretched gaussian noise firstly the hausdorff fractal metrics are introduced as an extension of non euclidean distance based on the fractal scaling the hausdorff derivative is derived which can describe the problems of interest to construct non integer differential equations secondly we introduce the hausdorff derivatives in tackling partial differential equations and the fundamental solution of hausdorff derivative diffusion equation is stretched gaussian distribution thirdly we analyze the feasibility of the least square method for stretched gaussian noise which obeys stretched gaussian distribution the least square method is inapplicable when the noise level is larger than 5 finally by using the hausdorff fractal distance we introduce the stretched least square method which improves the traditional least square method to fit stretched gaussian noise

super orthogonal space time trellis codes we introduce a new class of space time codes called super orthogonal space time trellis codes these codes combine set partitioning and a super set of orthogonal space time block codes in a systematic way to provide full diversity and improved coding gain over earlier space time trellis code constructions we also study the optimality of our set partitioning and provide coding gain analysis codes operating at different rates up to the highest theoretically possible rate for different number of states can be designed by using our optimal set partitioning super orthogonal space time trellis codes can provide a tradeoff between rate and coding gain simulation results show more than 2 db improvements over the codes presented in the literature while providing a systematic design methodology

a general method for calculating error probabilities over fading channels signal fading is a ubiquitous problem in mobile and wireless communications in digital systems fading results in bit errors and evaluating the average error rate under fairly general fading models and multichannel reception is often required predominantly to date most researchers perform the averaging using the probability density function method or the moment generating function mgf method this paper presents a third method called the characteristic function chf method for calculating the average error rates and outage performance of a broad class of coherent differentially coherent and noncoherent communication systems with or without diversity reception in a myriad of fading environments unlike the mgf technique the proposed chf method based on parseval s theorem enables us to unify the average error rate analysis of different modulation formats and all commonly used predetection diversity techniques i e maximal ratio combining equal gain combining selection diversity and switched diversity within a single common framework the chf method also lends itself to the averaging of the conditional error probability involving the complementary incomplete gamma function and the confluent hypergeometric function over fading amplitudes which heretofore resisted to a simple form as an aside we show some previous results as special cases of our unified framework

poisson overdispersion estimates based on the method of asymmetric maximum likelihood abstract a common difficulty in regression problems with poisson or binomial or other exponential family response variables is over dispersion the scatter around the fitted regression is too large by the standards of poisson variability this article concerns the description estimation and testing of various patterns of overdispersion with particular emphasis on the poisson case asymmetric maximum likelihood aml is a method of fitting regressions for the conditional percentiles of the response variable as a function of the predictors e g the conditional 90th percentile of y given x distances between the various regression percentiles give a direct assessment of overdispersion the discussion is carried through in terms of an archaeological data set where we see that the counts are overdispersed by a factor of 1 35 in one part of the covariate space but not at all in another moreover the overdispersion is about 40 larger in the positive response direction than in the negative the aml es

dirichlet process mixed generalized linear models abstract although generalized linear models glm s are an attractive and widely used class of models they are limited in the range of density shapes that they can provide for instance they are unimodal exponential families of densities in the response variable with tail behavior determined by the implicit mean variance relationship dirichlet process dp mixing adds considerable flexibility to these models using such mixing we develop models that we call dpmglm s which still retain the glm character with regard to the mean overdispersed glm s oglm s provide an alternative class of models to cope with extra variability in samples we show that how oglm s may be dp mixed leading to what we call dpmoglm s these models are extremely rich moreover recent computational advances enable them to be fitted straightforwardly we illustrate this with both simulated and real datasets we also address the question of choosing between the glm oglm dpmglm and dpmoglm finally we consider extensions by

a trivariate nakagami m distribution with arbitrary covariance matrix and applications to generalized selection diversity receivers this paper deals with a trivariate nakagami m distribution derived from the diagonal elements of a wishart matrix for this distribution infinite series representations for its probability density and cumulative distribution functions are derived having an arbitrary covariance matrix and integer order fading parameters moreover upper bounds on the error resulting from truncating the infinite series are obtained based on the derived formulas the performance of triple branch generalized selection combining gsc receivers is analyzed for this type of receivers the outage and the average bit error probability for a variety of modulation schemes are analytically obtained the performance of gsc receivers is compared to that of conventional selection and maximal ratio diversity schemes in order to check the accuracy and convergence of the derived formulas various performance evaluation results are presented and compared to equivalent simulation ones

novel simple representations for gaussian class multivariate distributions with generalized correlation novel single integral representations for the multivariate probability density functions and cumulative distribution functions of gaussian class distributions rayleigh rician weibull nakagami m and generalized rician are derived the solutions are expressed in terms of well known functions which are available in common mathematical software the marginal random variables are not necessarily identically distributed as is the case for some past solutions a generalized correlation structure based on a special linear transformation of independent gaussian random variables is used in this study the advantage of the new representation is that only a single integral computation is needed to compute an n dimensional distribution

parameter orthogonality and approximate conditional inference on propose une statistique du rapport de vraisemblance construite a partir de la distribution conditionnelle des observations etant donne les estimateurs du maximum de vraisemblance pour les parametres de nuisance

geometrically uniform codes a signal space code c is defined as geometrically uniform if for any two code sequences in c there exists an isometry that maps one sequence into the other while leaving the code c invariant geometrical uniformity a strong kind of symmetry implies such properties as a the distance profiles from code sequences in c to all other code sequences are all the same and b all voronoi regions of code sequences in c have the same shape it is stronger than ungerboeck zehavi wolf symmetry or calderbank sloane regularity nonetheless most known good classes of signal space codes are shown to be generalized coset codes and therefore geometrically uniform including a lattice type trellis codes based on lattice partitions lambda lambda such that z sup n lambda lambda 4z sup n is a lattice partition chain and b phase shift keying psk type trellis codes based on up to four way partitions of a 2 sup n psk signal set

on properties of the support of capacity achieving distributions for additive noise channel models with input cost constraints we study the classical problem of characterizing the channel capacity and its achieving distribution in a generic fashion we derive a simple relation between three parameters the input output function the input cost function and the noise probability density function one which dictates the type of the optimal input in layman terms we prove that the support of the optimal input is bounded whenever the cost grows faster than a cutoff growth rate equal to the logarithm of the inverse of the noise probability density function evaluated at the input output function furthermore we prove a converse statement that says whenever the cost grows slower than the cutoff rate the optimal input has necessarily an unbounded support in addition we show how the discreteness of the optimal input is guaranteed whenever the triplet satisfy some analyticity properties we argue that a suitable cost function to be imposed on the channel input is one that grows similarly to the cutoff rate our results are valid for any cost function that is super logarithmic they summarize a large number of previous channel capacity results and give new ones for a wide range of communication channel models such as gaussian mixtures generalized gaussians and heavy tailed noise models that we state along with numerical computations

the bivariate generalized κ κ g distribution and its application to diversity receivers the correlated bivariate generalized k kg distribution with not necessarily identical shaping and scaling parameters is introduced and studied this composite distribution is convenient for modeling multipath shadowing correlated fading environments when the correlations between the signal envelopes and their powers are different generic infinite series expressions are derived for the probability density function pdf the cumulative distribution function cdf and the joint moments assuming identical shaping parameters simpler expressions for the pdf cdf and the characteristic function cf are provided while the joint moments are derived in closed form furthermore the pdfs of the product and ratio of two correlated kg random variables are obtained capitalizing on these theoretical expressions for the statistical characteristics of the correlated kg distribution the performance analysis of various diversity reception techniques such as maximal ratio combining mrc equal gain combining egc and selection diversity sd over bivariate kg fading channels is presented for the sd the outage probability is studied while for the mrc and egc the average bit error probability is obtained the proposed analysis is accompanied by numerical results clearly demonstrating the usefulness of the theoretical approach as well as the appropriateness of the kg distribution to model multipath shadowing fading channels

beyond rock paper scissors systems deterministic models of cyclic ecological systems with more than three species abstract we consider cyclic ecological systems consisting of more than three species extending the well studied three species rock paper scissors rps system for such systems alliance and partial alliance states consisting of non competing species can form a phenomenon not present in classical rps systems we develop analyze and simulate a may leonard type model accounting for cyclic dynamics and spatial diffusion we analyze in detail four species and five species systems determine dynamics for both spatially homogeneous initial conditions i e ode models and the propagation and interaction of patches of different species driven by diffusion and the cyclic dynamics pde models we show markedly different behavior between the four and five species models with alliance states as stable steady states for the former whereas both coexistence of all species and heteroclinic cycles are possible stable outcomes for the latter finally we discuss the extension of this even odd split to systems with more than five species

complex predator invasion waves in a holling tanner model with nonlocal prey interaction abstract we consider predator invasions for the nonlocal holling tanner model predators are introduced in a small region adjacent to an extensive predator free region in its simplest form an invasion front propagates into the predator free region with a predator prey coexistence state displacing the predator free state however patterns may form in the wake of the invasion front due to instability of the coexistence state the coexistence state can be subject to either oscillatory or cellular instability depending on parameters furthermore the oscillatory instability can be either at zero wave number or finite wave number in addition the unstable predator free state can be subject to additional cellular instabilities when the extent of the nonlocality is sufficiently large we perform numerical simulations that demonstrate that the invasion wave may have a complex structure in which different spatial regions exhibit qualitatively different behaviors these regions are separated by relatively narrow transition regions that we refer to as fronts we also derive analytic approximations for the speeds of the fronts and find qualitative and quantitative agreement with the results of computations

error probability analysis of bit interleaved coded modulation this correspondence presents a simple method to accurately compute the error probability of bit interleaved coded modulation bicm thanks to the binary input output symmetric bios nature of the channel the pairwise error probability pep is equal to the tail probability of a sum of random variables with a particular distribution this probability is in turn computed with a saddlepoint approximation its precision is numerically validated for coded transmission over standard gaussian noise and fully interleaved fading channels for both convolutional and turbo like codes

ser of threshold based hybrid selection maximal ratio combining in correlated nakagami fading the average symbol error rate of threshold based hybrid selection maximal ratio combining t hs mrc with correlated nakagami m fading channels is obtained for positive integer values of fading parameter m for a special correlation structure an accurate approximate analysis of t hs mrc in arbitrarily correlated nakagami m fading channels is presented by using a green matrix approximation the derivation allows different m ary linear modulation schemes we illustrate our methodology using m ary phase shift keying as an example

design and analysis of bit interleaved coded space time modulation bit interleaved coded space time modulation bic stm is an attractive strategy to achieve high power and bandwidth efficiency over multiple input and multiple output mimo fading channels due to coding and diversity gains promised by the serial concatenation of an outer convolutional code a bitwise interleaver and an inner high order space time modulation stm in this paper bicstm with iterative decoding bicstm id including non iterative decoding as a special case is considered for designing the inner stm two parameters based on bitwise pairwise error probabilities b pep for the cases with and without a priori knowledge are proposed as new measures for designing labeling rules for the stm codewords set suited to iterative decoding on the other hand the bicstm id scheme is analyzed from an information theoretical aspect and information processing characteristic ipc analysis is developed for mimo systems in order to fully characterize the bicstm id scheme based on a new equivalent model of combined binary input channels the analysis results show that the ipc analysis offers a unified perspective for bicstm and bicstm id from an information theoretical point of view and provides a comprehensive insight into the whole bicstm id scheme as well additionally ipc based upper and lower bounds on bit error ratio ber performance are extended to bicstm id and are confirmed by simulations these bounds are of significant practical interest for estimating the ber performance of the bit interleaved concatenated schemes with general nonlinear inner systems

on the snr penalty of mpsk with hybrid selection maximal ratio combining over i i d rayleigh fading channels closed form expressions that lower and upper bound the penalty of hybrid selection maximal ratio combining relative to maximal ratio combining mrc for m ary phase shift keying mpsk modulation are proved the bounds offer simple to evaluate explicit expressions and are typically within 0 6 db for hybrid systems with diversity order up to eight that use at least two branches yet are independent of signal to noise ratio snr contrary to conclusions conjectured in a previously published paper it is proved that the snr penalty is not a constant independent of snr it is also shown that previous estimates of the performance losses of selection diversity relative to mrc underestimate or lower bound the losses for mpsk modulation systems and that the true loss can be significantly larger than previously believed an upper bound to this loss is also obtained

performance analysis for bicm transmission over gaussian mixture noise fading channels bit interleaved coded modulation bicm has been adopted in many systems and standards for spectrally efficient coded transmission the analytical evaluation of bicm performance parameters in particular bit error rate ber has received considerable attention in the recent past in this paper we derive ber approximations for bicm transmission over general fading channels impaired by gaussian mixture noise gmn to this end we build upon the saddlepoint approximation of the pairwise error probability pep and a recently established approximation for the probability density function pdf of bit wise reliability metrics for nonfading additive white gaussian noise awgn channels we extend this pdf approximation to the case of gmn and obtain closed form expressions for its laplace transform for fading gmn channels the latter allows us to express the pep and thus ber via the saddlepoint approximation for the special case of fading awgn channels the presented approximations are closed form since the saddlepoint is well approximated by 1 2 for bicm decoding furthermore we derive closed form pep expressions also for gmn channels in the high signal to noise ratio regime and establish the diversity and coding gain for bicm transmission over fading gmn channels selected numerical results for the ber of convolutional coded bicm highlight the usefulness of the proposed approximations and the differences between awgn and gmn channels

gaussian class multivariate weibull distributions theory and applications in fading channels ascertaining on the suitability of the weibull distribution to model fading channels a theoretical framework for a class of multivariate weibull distributions originated from gaussian random processes is introduced and analyzed novel analytical expressions for the joint probability density function pdf moment generating function mgf and cumulative distribution function cdf are derived for the bivariate distribution of this class with not necessarily identical fading parameters and average powers two specific distributions with arbitrary number of correlated variates are considered and studied with exponential and with constant correlation where their pdfs are introduced both cases assume equal average fading powers but not necessarily identical fading parameters for the multivariate weibull distribution with exponential correlation useful corresponding formulas as for the bivariate case are derived the presented theoretical results are applied to analyze the performance of several diversity receivers employed with selection equal gain and maximal ratio combining mrc techniques operating over correlated weibull fading channels for these diversity receivers several useful performance criteria such as the moments of the output signal to noise ratio snr including average output snr and amount of fading and outage probability are analytically derived moreover the average symbol error probability for several coherent and noncoherent modulation schemes is studied using the mgf approach the proposed mathematical analysis is complemented by various evaluation results showing the effects of the fading severity as well as the fading correlation on the diversity receivers performance

computer assisted analysis of mixtures c a man statistical algorithms summary this paper presents various algorithmic approaches for computing the maximum likelihood estimator of the mixing distribution of a one parameter family of densities and provides a unifying computeroriented concept for the statistical analysis of unobserved heterogeneity i e observations stemming from different subpopulations in a univariate sample the case with unknown number of population subgroups as well as the case with known number of population subgroups with emphasis on the first is considered in the computer package c a man computer assisted mixture analysis it includes an algorithmic menu with choices of the em algorithm the vertex exchange algorithm a combination of both as well as the vertex direction method to ensure reliable convergence a steplength menu is provided for the three latter methods each achieving monotonicity for the direction of choice c a man has the option to work with restricted support size that is the case when the number of components is known a priori in the latter case the em algorithm is used applications of mixture modelling in medical problems are discussed

approximate performance analysis of coded ostbc ofdm systems over arbitrary correlated generalized ricean fading channels a framework for analyzing the performance of coded ostbc ofdm systems over arbitrary correlated generalized ricean fading channels is established the moment generating function of the signal to noise ratio at the input to the channel decoder is derived assuming correlated transmitter and receiver antennas and correlated paths in frequency selective channels the probability of outage the pairwise error probability and the bit error rate are then evaluated bit interleaved and iteratively decoded turbo product codes gray encoded m ary quadrature amplitude modulation and other parameters of the ieee 802 16 standard are used to illustrate numerical results

asymptotic performance of hybrid selection maximal ratio combining over fading channels in this letter we study the asymptotic performance of hybrid selection maximal ratio combining hs mrc and postdetection hs equal gain combining hs egc over generalized fading channels for large average signal to noise ratios asnrs by evaluating the asymptotic moment generating function of the hs mrc output snr at high asnr we derive the diversity and coding gains for hs mrc for a large class of modulation formats and versatile fading conditions including different types of fading channels and nonidentical snr statistics across diversity branches our analytical results reveal that the diversity gains of hs mrc and hs egc are equivalent to that of mrc and the difference in the coding gains for different modulation formats is manifested in terms of a modulation factor defined in this letter some new analytical results about effects of the number of combined branches for hs mrc and noncoherent combining loss of hs egc are also provided

absolute and convective instabilities of waves on unbounded and large bounded domains abstract instabilities of nonlinear waves on unbounded domains manifest themselves in different ways an absolute instability occurs if the amplitude of localized wave packets grows in time at each fixed point in the domain in contrast convective instabilities are characterized by the fact that even though the overall norm of wave packets grows in time perturbations decay locally at each given point in the unbounded domain wave packets are convected towards infinity in experiments as well as in numerical simulations bounded domains are often more relevant we are interested in the effects that the truncation of the unbounded to a large but bounded domain has on the aforementioned in stability properties of a wave these effects depend upon the boundary conditions that are imposed on the bounded domain we compare the spectra of the linearized evolution operators on unbounded and bounded domains for two classes of boundary conditions it is proved that periodic boundary conditions reproduce the point and essential spectrum on the unbounded domain accurately spectra for separated boundary conditions behave in quite a different way firstly separated boundary conditions may generate additional isolated eigenvalues secondly the essential spectrum on the unbounded domain is in general not approximated by the spectrum on the bounded domain instead the so called absolute spectrum is approximated that corresponds to the essential spectrum on the unbounded domain calculated with certain optimally chosen exponential weights we interpret the difference between the absolute and the essential spectrum in terms of the convective behavior of the wave on the unbounded domain in particular it is demonstrated that the stability of the absolute spectrum implies convective instability of the wave but that convectively unstable waves can destabilize under domain truncation the theoretical predictions are compared with numerical computations

on the inverse symbol error probability for diversity reception this paper addresses the problem of finding the inverse symbol error probability sep expression for coherent detection of m ary phase shift keying with multichannel reception and maximal ratio combining in rayleigh fading to this aim we derive upper and lower bounds on sep that are simply invertible and uniformly tight for all values of signal to noise ratio this enables us to obtain tight bounds on the inverse sep and on the symbol error outage seo i e sep based outage probability as an example of application to digital mobile radio the seo in a log normal shadowing environment is analyzed

performance of optimum and suboptimum receivers in the presence of impulsive noise modeled as an alpha stable process impulsive noise bursts in communication systems are traditionally handled by incorporating in the receiver a limiter which clips the received signal before integration an empirical justification for this procedure is that it generally causes the signal to noise ratio to increase recently very accurate models of impulsive noise were presented based on the theory of symmetric spl alpha stable probability density functions we examine the performance of optimum receivers designed to detect signals embedded in impulsive noise which is modeled as an infinite variance symmetric spl alpha stable process and compare it against the performance of several suboptimum receivers as a measure of receiver performance we compute an asymptotic expression for the probability of error for each receiver and compare it to the probability of error calculated by extensive monte carlo simulation

spatial scan statistics with overdispersion the spatial scan statistic has been widely used in spatial disease surveillance and spatial cluster detection for more than a decade however overdispersion often presents in real world data causing not only violation of the poisson assumption but also excessive type i errors or false alarms in order to account for overdispersion we extend the poisson based spatial scan test to a quasi poisson based test the simulation shows that the proposed method can substantially reduce type i error probabilities in the presence of overdispersion in a case study of infant mortality in jiangxi china both tests detect a cluster however a secondary cluster is identified by only the poisson based test it is recommended that a cluster detected by the poisson based scan test should be interpreted with caution when it is not confirmed by the quasi poisson based test copyright 2011 john wiley sons ltd

on first order markov modeling for the rayleigh fading channel previous models for the received signal amplitude of the flat fading channel that use first order finite state markov chains are examined the stochastic properties of a proposed first order model based on these models are examined the limitations of using an information theoretic metric which is sometimes used to justify a first order markov chain as a sufficient model for very slowly fading channels are discussed a simple method of qualitatively comparing autocorrelation functions is instead proposed the usefulness of the first order markov chain in representing the flat fading channel is examined by looking at two specific problems in wireless system applications that represent two disparate cases the first case involves analysis over a short duration of time relative to the inverse of the normalized doppler frequency while the second involves analysis over a long duration of time contrary to previous reports the results indicate that first order markov chains are not generally suitable for very slowly fading channels rather first order markov chains can be suitable for very slowly fading applications which require analysis over only a short duration of time

error probability bounds for bit interleaved space time trellis coding over block fading channels in this correspondence we investigate the error probability bounds of a bit interleaved space time trellis coding bisttc scheme which concatenates bit interleaved coded modulation bicm with a space time trellis code sttc we focus on general block fading channels wherein each data packet or frame spans a number of independent fading blocks bicm applied to such channel environments can effectively exploit both time and frequency selectivity while a sttc maximizes the spacial diversity order the exact pairwise error probability pep and weight enumeration function wef of bisttc are used to evaluate the error bound due to the concatenation of an outer error correction code ecc and a sttc the overall wef of bisttc is obtained by combining the wef of the outer code with that of the sttc through an uniform interleaver the main challenge here is to compute the wef of a sttc for block fading channels with reasonable complexity we rely on constructing a composite state transition matrix based on a number of single step virtual trellises each corresponding to an independent fading block within a frame we discuss how this approach reduces storage and computational requirements in the bound analysis compared to the existing method of obtaining the state transition matrix through accumulation of single step transition matrices the derived bound is applicable to both spatially uncorrelated and correlated channels as well as to both flat and frequency selective block fading channels the bound is shown to provide a reasonably close estimate of the simulated performance based on the turbo equalizer like iterative processing of soft information between the sttc decoder and the ecc decoder

on crb for parameter estimation in two component gaussian mixtures and the impact of misspecification a closed form expression for the cramer rao lower bound crb for parameter estimation in the presence of a two component gaussian mixture noise model is derived it is further shown that this closed form expression can be lower bounded by a simple two term expression closed form expressions are also derived for the variance of the maximum likelihood estimator mle when the parameters of the gaussian mixture model are misspecified it is then shown that the mle can handle a significant amount of misspecification of the parameters of the gaussian mixture model and yet maintain a variance close to the crb

space time block codes from orthogonal designs we introduce space time block coding a new paradigm for communication over rayleigh fading channels using multiple transmit antennas data is encoded using a space time block code and the encoded data is split into n streams which are simultaneously transmitted using n transmit antennas the received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise maximum likelihood decoding is achieved in a simple way through decoupling of the signals transmitted from different antennas rather than joint detection this uses the orthogonal structure of the space time block code and gives a maximum likelihood decoding algorithm which is based only on linear processing at the receiver space time block codes are designed to achieve the maximum diversity order for a given number of transmit and receive antennas subject to the constraint of having a simple decoding algorithm the classical mathematical framework of orthogonal designs is applied to construct space time block codes it is shown that space time block codes constructed in this way only exist for few sporadic values of n subsequently a generalization of orthogonal designs is shown to provide space time block codes for both real and complex constellations for any number of transmit antennas these codes achieve the maximum possible transmission rate for any number of transmit antennas using any arbitrary real constellation such as pam for an arbitrary complex constellation such as psk and qam space time block codes are designed that achieve 1 2 of the maximum possible transmission rate for any number of transmit antennas for the specific cases of two three and four transmit antennas space time block codes are designed that achieve respectively all 3 4 and 3 4 of maximum possible transmission rate using arbitrary complex constellations the best tradeoff between the decoding delay and the number of transmit antennas is also computed and it is shown that many of the codes presented here are optimal in this sense as well

performance analysis of ldpc coded diversity combining on rayleigh fading channels with impulsive noise spatial diversity is an effective method to mitigate the effects of fading and when used in conjunction with low density parity check ldpc codes it can achieve excellent error correcting performance noise added at each branch of the diversity combiner is generally assumed to be additive white gaussian noise but there are many applications where the received signal is impaired by noise with a non gaussian distribution in this paper we derive the exact bit error probability of different linear combining techniques on rayleigh fading channels with impulsive noise which is modeled using symmetric alpha stable distributions the relationship for the signal to noise ratios of these linear combiners is derived and then different non linear detectors are presented a detector based on the bi parameter cauchy gaussian mixture model is used and shows near optimal performance with a significant reduction in complexity when compared with the optimal detector furthermore the threshold signal to noise ratio of ldpc codes for different combining techniques on these channels is derived using density evolution and an estimation of the waterfall performance of ldpc codes is derived that reduces the gap between simulated and asymptotic performance

pattern formation in a model of competing populations with nonlocal interactions abstract we analyze and compute an extension of a previously developed population model based on the well known diffusive logistic equation with nonlocal interaction to a system involving competing species our model involves a system of nonlinear integro differential equations with the nonlocal interaction characterized by convolution integrals of the population densities against specified kernel functions the extent of the nonlocal coupling is characterized by a parameter so that when 0 the problem becomes local we consider critical points of the model i e spatially homogeneous equilibrium solutions there is generally one critical point in the first quadrant i e both population densities positive denoting coexistence of the two species we show that this solution can be destabilized by the nonlocal coupling and obtain general conditions for stability of this critical point as a function of the specific kernel function and parameters of the model we study the nonlinear behavior of the model and show that the populations can evolve to localized cells or islands we find that the stability transition is supercritical near the stability boundary solutions are small amplitude nearly sinusoidal oscillations however when increases large amplitude nonlinear states are found we find a multiplicity of stable steady state patterns we further show that with a stepfunction kernel function the structure of these islands a highly nonlinear phenomenon can be described analytically finally we analyze the role of the kernel function and show that for some choices of kernel function the resulting population islands can exhibit tip splitting behavior and island amplitude modulation

asymptotical performance of m ary and binary signals over multipath multichannel rayleigh and rician fading this paper presents a general framework for computing the asymptotic error probability i e at high average snrs of m ary and binary signaling schemes over rician and rayleigh fading diversity channels a general theorem theorem 1 relates the asymptotic error rate of multipath and multichannel receivers over awgn isi free channels to the multidimensional integral of the conditional error probability two other theorems are presented for the particular cases where the conditional error probability is a function of the sum of received snrs theorem 2 or received amplitudes theorem 3 theorems 2 and 3 are related for linear coherent systems and closed form expressions are obtained for equal gain combining systems detection structures for typical diversity schemes coherent noncoherent maximal ratio and equal gain combining and quadratic noncoherent combining are considered we analyze the asymptotic error rates of some m ary signaling schemes mpsk mpam with kth order diversity and orthogonal signals with k 1 and with coherent and noncoherent detection binary signaling is also considered in our study

asymptotic analysis of coherent and differential space time codes in non gaussian noise and interference in this paper we provide a unified framework for the asymptotic performance analysis of space time codes stcs in correlated ricean fading and non gaussian noise and interference in particular we derive simple and asymptotically tight expressions for the pairwise error probability pep of coherent and differential stcs which are valid for any type of noise and interference with finite moments and detection with general mahalonobis distance md metrics including euclidean distance ed and noise decorrelating nd metrics these pep expressions can be combined with truncated union bounds to obtain accurate asymptotic approximations for the bit symbol and frame error probabilities of stcs we show that while the diversity gain of an stc is independent of the type of noise and the type of md metric used the coding gain is not and depends on certain moments of the noise and interference we provide closed form expressions for these moments for several practically relevant types of noise and interference we show that for correlated noise significant performance gains can be achieved with the nd metric compared to the ed metric while noise correlations are beneficial at high signal to noise ratios if they can be exploited by the metric they are harmful if this is not the case and the simple ed metric is employed all our analytical findings are confirmed by simulations for various popular stcs and several different types of noise and interference

construction of multiblock space time codes from division algebras with roots of unity as nonnorm elements the authors give a construction of multiblock space time block codes from cyclic division algebras with a given nth root of unity as the nonnorm element the construction uses local class field theory multiblock codes with m blocks can achieve an m fold increase in diversity

analysis of switched diversity systems on generalized fading channels the performances of switched diversity systems operating on generalized nakagami fading channels are analyzed using a discrete time model the average bit error rate ber of binary noncoherent frequency shift keying ncfsk on slow nonselective nakagami fading channels is derived closed form expressions that can be used to determine optimum switching thresholds in a minimum error rate sense are also derived in addition the use of optimum fixed thresholds is considered it is found that a considerable amount of diversity gain can be obtained using an optimum fixed rather than adaptive switching threshold results are obtained for both independent and correlated nakagami fading branch signals the effects of fading severity and the correlation coefficient on both the ber and on the optimum switching threshold are investigated it is shown that useful diversity gain can be obtained with power correlation coefficients as high as 0 9 when the fading is strong the results for a rayleigh channel are obtained and presented as a special case of generalized fading model

multilevel codes theoretical concepts and practical design rules this paper deals with 2 sup l ary transmission using multilevel coding mlc and multistage decoding msd the known result that mlc and msd suffice to approach capacity if the rates at each level are appropriately chosen is reviewed using multiuser information theory it is shown that there is a large space of rate combinations such that mlc and full maximum likelihood decoding mld can approach capacity it is noted that multilevel codes designed according to the traditional balanced distance rule tend to fall in the latter category and therefore require the huge complexity of mld the capacity rule the balanced distances rules and two other rules based on the random coding exponent and cutoff rate are compared and contrasted for practical design simulation results using multilevel binary turbo codes show that capacity can in fact be closely approached at high bandwidth efficiencies moreover topics relevant in practical applications such as signal set labeling dimensionality of the constituent constellation and hard decision decoding are emphasized bit interleaved coded modulation proposed by caire et al see ibid vol 44 p 927 46 1998 is reviewed in the context of mlc finally the combination of signal shaping and coding is discussed significant shaping gains are achievable in practice only if these design rules are taken into account

new series representation for the trivariate non central chi squared distribution this paper derives a new infinite series representation for the trivariate non central chi squared distribution when the underlying correlated gaussian variables have a tridiagonal form of an inverse covariance matrix the joint probability density function is derived using miller s approach and dougall s identity moreover the trivariate cumulative distribution function cdf and characteristic function chf are also derived finally the bivariate non central chi squared distribution and some known forms are shown to be special cases of the more general distribution however the derivation of non central chi squared distribution for an arbitrary covariance matrix seems intractable via miller s approach two applications of the newly derived results are provided for performance analysis of multiple input multiple output mimo systems with transmit antenna selection over a correlated rician fading environment some numerical results are also presented to verify the accuracy of the analytical expressions

performance of bicm sc and bicm ofdm systems with diversity reception in non gaussian noise and interference in this paper we present a general mathematical framework for performance analysis of single carrier sc and orthogonal frequency division multiplexing ofdm systems employing popular bit interleaved coded modulation bicm and multiple receive antennas the proposed analysis is applicable to bicm systems impaired by general types of fading including rayleigh ricean nakagami m nakagami q and weibull fading and general types of noise and interference with finite moments such as additive white gaussian noise awgn additive correlated gaussian noise gaussian mixture noise co channel interference narrowband interference and ultra wideband interference we present an approximate upper bound for the bit error rate ber and an accurate closed form approximation for the asymptotic ber at high signal to noise ratios for viterbi decoding with the standard euclidean distance branch metric for the standard rate 1 2 convolutional code the proposed approximate upper bound and the asymptotic approximation become tight at bers of 10 6 and 10 12 respectively however if the code is punctured to higher rates e g 2 3 or 3 4 the asymptotic approximation also becomes tight at a ber of 10 6 exploiting the asymptotic ber approximation we show that the diversity gain of bicm systems only depends on the free distance of the code the type of fading and the number of receive antennas but not on the type of noise in contrast their coding gain strongly depends on the noise moments our asymptotic analysis shows that as long as the standard euclidean distance branch metric is used for viterbi decoding bicm systems optimized for awgn are also optimum for any other type of noise and interference with finite moments

performance and optimization of network coded cooperative diversity systems in this paper we study network coded cooperative diversity nccd systems comprising multiple sources one relay and one destination where the relay detects the packets received from all sources and performs galois field gf network coding over rm gf 2 m before forwarding a single packet to the destination assuming independent rayleigh fading for all links of the network we derive simple and accurate closed form approximations for the asymptotic symbol and bit error rates of nccd systems the derived error rate expressions are valid for arbitrary numbers of sources arbitrary modulation schemes and arbitrary constellation mappings and provide significant insight into the impact of various system and channel parameters on performance moreover these expressions can be exploited for optimization of the constellation mapping as well as for formulation of various nccd system optimization problems including optimal power allocation relay selection and relay placement

asymptotic performance of generalized selection combining in generic noise and fading in this letter we investigate the performance of generalized selection combining in channels impaired by generalized fading and generic noise with finite moments in particular we derive accurate high signal to noise ratio approximations for the bit and symbol error rates of linear modulation schemes which offer significant insight into the impact of the number of selected diversity branches the type of fading and the type of noise our analysis is applicable to all practically relevant types of fading including rayleigh rician nakagami q and nakagami m fading all types of noise with finite moments including gaussian noise gaussian mixture noise generalized gaussian noise and co channel interference and non identically distributed fading and noise across the diversity branches our results reveal that while performance always improves with increasing number of selected branches for identically distributed noise this is not necessarily true for non identically distributed noise

residual diagnostics for mixture models abstract a sample is commonly modeled by a mixture distribution if the observations follow a common distribution but the parameter of interest differs between observations for example we observe the lengths but not the ages of a sample offish it may be reasonable to assume that length is normally distributed about an unknown mean that depends on the age of the fish provided there is more than one age class in the sample then the data are distributed as a mixture of normals in this article we assume that the data are a random sample from a mixture of exponential family distributions and that for each observation the parameter of interest is sampled independently from an unknown mixing distribution q the adequacy of a fitted mixture model can be assessed by examining residuals based on the ratio of the observed to expected fit residuals based on the homogeneity model in which q is a one point distribution display a convexity property when the data follow a mixture model this becomes the basis fo

comments on bit interleaved coded modulation caire taricco and biglieri presented a detailed analysis of bit interleaved coded modulation bicm a simple and popular technique used to improve system performance especially in the context of fading channels they derived an upper bound to the probability of error called the expurgated bound in this correspondence the proof of the expurgated bound is shown to be flawed a new upper bound is also derived it is not known whether the original expurgated bound is valid for the important special case of square qam with gray labeling but the new bound is very close to and slightly tighter than the original bound for a numerical example

performance of dual selection combiners over correlated nakagami m fading with different fading parameters this letter presents infinite series expressions for the outage probability the probability density function the average error probability for binary modulations and the average signal to noise ratio of dual selection combiners over correlated fading with arbitrary fading parameters at each input of the combiner the outage probability is calculated for both thermal noise and interference limited scenarios the results obtained for the outage probabilities specified for identical fading parameters at both branches of the combiner are contrasted with the results of other studies in the literature

achieving full frequency and space diversity in wireless systems via bicm ofdm stbc and viterbi decoding orthogonal frequency division multiplexing ofdm is known as an efficient technique to combat frequency selective channels in this paper we show that the combination of bit interleaved coded modulation bicm and ofdm achieves the full frequency diversity offered by a frequency selective channel with any kind of power delay profile pdp conditioned on the minimum hamming distance dfree of the convolutional code this system has a simple viterbi decoder with a modified metric we then show that by combining such a system with space time block coding stbc one can achieve the full space and frequency diversity of a frequency selective channel with n transmit and m receive antennas bicm stbc ofdm achieves the maximum diversity order of nml over l tap frequency selective channels regardless of the pdp of the channel this latter system also has a simple viterbi decoder with a properly modified metric we verify our analytical results via simulations including channels employed in the ieee 802 11 standards

on circularity circularity is an assumption that was originally introduced for the definition of the probability distribution function of complex normal vectors however this concept can be extended in various ways for nonnormal vectors the first purpose of the paper is to introduce and compare some possible definitions of circularity from these definitions it is also possible to introduce the concept of circular signals and to study whether or not the spectral representation of stationary signals introduces circular components therefore the relationships between circularity and stationarity are analyzed in detail finally the theory of linear mean square estimation for complex signals exhibits some connections with circularity and it is shown that without this assumption the estimation theory must be reformulated

linear estimation of correlated data in wireless sensor networks with optimum power allocation and analog modulation in this paper we study the energy efficient distributed estimation problem for a wireless sensor network where a physical phenomena that produces correlated data is sensed by a set of spatially distributed sensor nodes and the resulting noisy observations are transmitted to a fusion center via noise corrupted channels we assume a gaussian network model where i the data samples being sensed at different sensors have a correlated gaussian distribution and the correlation matrix is known at the fusion center ii the links between the local sensors and the fusion center are subject to fading and additive white gaussian noise awgn and the fading gains are known at the fusion center and iii the central node uses the squared error distortion metric we consider two different distortion criteria i individual distortion constraints at each node and ii average mean square error distortion constraint across the network we determine the achievable power distortion regions under each distortion constraint taking the delay constraint into account we investigate the performance of an uncoded transmission strategy where the noisy observations are only scaled and transmitted to the fusion center at the fusion center two different estimators are considered i the best linear unbiased estimator blue that does not require knowledge of the correlation matrix and ii the minimum mean square error mmse estimator that exploits the correlations for each estimation method we determine the optimal power allocation that results in a minimum total transmission power while satisfying some distortion level for the estimate under both distortion criteria the numerical comparisons between the two schemes indicate that the mmse estimator requires less power to attain the same distortion provided by the blue and this performance gap becomes more dramatic as correlations between the observations increase furthermore comparisons between power distortion region achieved by the theoretically optimum system and that achieved by the uncoded system indicate that the performance gap between the two systems becomes small for low levels of correlation between the sensor observations if observations at all sensor nodes are uncorrelated the uncoded system with mmse estimator attains the theoretically optimum system performance

infinite series representations of the trivariate and quadrivariate rayleigh distribution and their applications few theoretical results are known about the joint distribution of three or more arbitrarily correlated rayleigh random variables rvs consequently theoretical performance results are unknown for three and four branch equal gain combining egc selection combining sc and generalized sc gsc in correlated rayleigh fading this paper redresses this gap by deriving new infinite series representations for the joint probability density function pdf and the joint cumulative distribution function cdf of three and four correlated rayleigh rvs bounds on the error resulting from truncating the infinite series are derived a classical approach due to miller is used to derive our results unfortunately miller s approach cannot be extended to more than four variates and in fact the quadrivariate case considered in this paper appears to be the most general result possible for brevity we treat only a limited number of applications in this paper the new pdf and cdf expressions are used to derive the outage probability of three branch sc the moments of the egc output signal to noise ratio snr and the moment generating function of the gsc 2 3 output snr in arbitrarily correlated rayleigh fading a novel application of bonferroni s inequalities allows new outage bounds for multibranch sc in arbitrarily correlated rayleigh channels

overdispersion diagnostics for generalized linear models abstract generalized linear models glm s are simple convenient models for count data but they assume that the variance is a specified function of the mean although overdispersed glm s allow more flexible mean variance relationships they are often not as simple to interpret nor as easy to fit as standard glm s this article introduces a convexity plot or c plot for short that detects overdispersion and relative variance curves and relative variance tests that help to understand the nature of the overdispersion convexity plots sometimes detect overdispersion better than score tests and relative variance curves and tests sometimes distinguish the source of the overdispersion better than score tests

unified asymptotic analysis of linearly modulated signals in fading non gaussian noise and interference in this paper we present a unified asymptotic symbol error rate ser analysis of linearly modulated signals impaired by fading and possibly non gaussian noise which in our definition also includes interference the derived asymptotic closed form results are valid for a large class of fading and noise processes our analysis also encompasses diversity reception with equal gain and selection combining and is extended to binary orthogonal modulation we show that for high signal to noise ratios snrs the ser of linearly modulated signals depends on the mellin transform of the probability density function pdf of the noise since the mellin transform can be readily obtained for all commonly encountered noise pdfs the provided ser expressions are easy and fast to evaluate furthermore we show that the diversity gain only depends on the fading statistic and the number of diversity branches whereas the combining gain depends on the modulation format the type of fading the number of diversity branches and the type of noise an exception are systems with a diversity gain of one since their combining gain and asymptotic ser are independent of the type of noise however in general in a log log scale for high snr the ser curves for different types of noise are parallel but not identical and their relative shift depends on the mellin transforms of the noise pdfs

spatial structures and periodic travelling waves in an integro differential reaction diffusion population model an integro differential reaction diffusion equation is proposed as a model for populations where local aggregation is advantageous but intraspecific competition increases as global populations increase it is claimed that this is inherently more realistic than the usual kind of reaction diffusion model for mobile populations three kinds of bifurcation from the uniform steady state solution are considered i to steady spatially periodic structures ii to periodic standing wave solutions and iii to periodic travelling wave solutions these correspond to aggregation and motion of populations

variable selection and model averaging in semiparametric overdispersed generalized linear models we express the mean and variance terms in a double exponential regression model as additive functions of the predictors and use bayesian variable selection to determine which predictors enter the model and whether they enter linearly or flexibly when the variance term is null we obtain a generalized additive model which becomes a generalized linear model if the predictors enter the mean linearly the model is estimated using markov chain monte carlo simulation and the methodology is illustrated using real and simulated data sets

error performance of multi antenna receivers in a poisson field of interferers a stochastic geometry approach in this paper we introduce an analytical framework for performance analysis and design of single input multiple output simo wireless systems in the presence of noise fading and radio frequency interference produced by randomly distributed active interferers surrounding an intended probe receiver the framework leverages recent application of stochastic geometry and poisson point processes ppps theory to network interference modeling to assess the impact of spatial dependence across multiple receive antennas three models of network interference are studied i the isotropic model where all receive antennas see interferers belonging to the same ppp ii the independent model where each receive antenna sees interferers belonging to an independent ppp and iii the mixture model which is a superposition of isotropic and independent interferences depending on the fading distribution of the interferers the nakagami m fading parameter of the probe link and the number of receive antennas either exact or upper bound formulas of the error probability averaged over noise fading and spatial interference are given our analysis shows that depending on the interference model performance can either improve or get worse with multiple antennas at the receiver the proposed analytical methodology is applicable to single and multi ppps interference environments

unveiling turbo codes some results on parallel concatenated coding schemes a parallel concatenated coding scheme consists of two simple constituent systematic encoders linked by an interleaver the input bits to the first encoder are scrambled by the interleaver before entering the second encoder the codeword of the parallel concatenated code consists of the input bits to the first encoder followed by the parity check bits of both encoders this construction can be generalized to any number of constituent codes parallel concatenated schemes employing two convolutional codes as constituent codes in connection with an iterative decoding algorithm of complexity comparable to that of the constituent codes have been previously shown to yield remarkable coding gains close to theoretical limits they have been named and are known as turbo codes we propose a method to evaluate an upper bound to the bit error probability of a parallel concatenated coding scheme averaged over all interleavers of a given length the analytical bounding technique is then used to shed some light on some crucial questions which have been floating around in the communications community since the proposal of turbo codes

anomalous spreading in a system of coupled fisher kpp equations abstract in this article we report on the curious phenomena of anomalous spreading in a system of coupled fisher kpp equations when a single parameter is set to zero the system consists of two uncoupled fisher kpp equations which give rise to traveling fronts propagating with the unique minimal kpp speed when the coupling parameter is nonzero various behaviors can be observed anomalous spreading occurs when one component of the system spreads at a speed significantly faster in the coupled system than it does in isolation while the speed of the second component remains unchanged we study these anomalous spreading speeds and show that they arise due to poles of the pointwise green s function corresponding to the linearization about the unstable homogeneous state these poles lead to anomalous spreading in the linearized system and come in two varieties one that persists and leads to anomalous spreading for the nonlinear system and one that does not we describe mechanisms leading to these two behaviors and prove that one class of poles are irrelevant as far as nonlinear wavespeed selection is concerned finally we show that the same mechanism can give rise to anomalous spreading even when the slower component does not spread

robust l_p norm decoding for bicm based secondary user systems the frequency bands used by secondary user systems such as cognitive radio and ultra wideband uwb systems are subject to various forms of non gaussian noise and interference including co channel and narrowband interference caused by the primary user and other secondary users as well as man made impulsive noise for secondary user systems employing popular bit interleaved coded modulation bicm we propose a robust lp norm metric for viterbi decoding to overcome the harmful effects of non gaussian noise and interference for the resulting system we derive an approximate upper bound on the bit error rate ber and a general analytical expression for the asymptotic ber valid for all practically relevant types of fading including rayleigh ricean nakagami m nakagami q and weibull fading and all types of noise and interference with finite moments simulation and analytical results show that in non gaussian noise and interference the proposed lp norm metric yields large performance gains over the conventional l2 norm metric and outperforms erasure decoding

spatio temporal structures in a differential flow reactor with cubic autocatalator kinetics abstract a model of a differential flow reactor with gray scott kinetics is considered in which the reactant is immobilised while the autocatalyst is allowed to flow with uniform velocity and to diffuse a linear stability analysis shows that there is a critical flow rate above which the spatially uniform stationary state is convectively unstable a weakly nonlinear analysis close to criticality results in a complex ginzburg landau equation cgle which governs the envelope amplitude of the packet of differential flow induced waves being the first derivation of such a modulation equation for such a problem the analysis of the cgle shows that this bifurcation is supercritical with proparating wave packets developing for flow rates above the critical value and identifies a region of parameter space close to the hopf bifurcation in the kinetic scheme where more complex propagating wave structures can arise the theoretical predictions are confirmed by numerical integrations of the initial value problem which also give results for flow rates well in excess of those amenable to analysis

tight error bounds for space time orthogonal block codes under slow rayleigh flat fading the performance of space time orthogonal block stob codes over slow rayleigh fading channels and maximum likelihood ml decoding is investigated two bonferroni type bounds one upper bound and one lower bound for the symbol error rate ser and bit error rate ber of the system are obtained the bounds are expressed in terms of the pairwise error probabilities peps and the two dimensional pairwise error probabilities 2 d peps of the transmitted symbols furthermore the bounds can be efficiently evaluated and they hold for arbitrary nonstandard signaling schemes and mappings numerical results demonstrate that the bounds are very accurate in estimating the performance of stob codes in particular the upper and lower bounds often coincide even at low channel signal to noise ratios large constellation sizes and large diversity orders

a note on overdispersed exponential families abstract the issue of creating overdispersion in a given one parameter one dimensional exponential family by extending it to a two parameter exponential family with the same support is considered an easily verifiable sufficient condition for this is derived it is shown that a large class of families satisfy this condition and that this class includes efron s 1986 and lindsay s 1986 family as special cases this class is also closely related to jorgensen s 1988 exponential dispersion models ump unbiased tests for testing overdispersion are exhibited and it is shown that in this context cox s overdispersion test is a special case a graphical display is developed to select a family of the general class which should be used with a given set of data to overdisperse a given target one parameter family two real data illustrations are given kr

application of perfect space time codes pep bounds and some practical insights the design of perfect space time codes constructed from cyclic division algebra cda on the quasi static mimo channel has received lots of attention in industry over the last few years however the recent standards that use multiple antennas terminals such as ieee 802 11n ieee 802 16e or lte are based on more realistic assumptions involving the use of outer codes and multi taps channels in this paper the question regarding the utility of using a high dimensional modulation schemes such as space time codes in a standard context is addressed for this we evaluate the performance of the perfect space time codes in term of an upper bound on the pairwise error probability and we compare it to the one of simple spatial division multiplexing sdm schemes finally simulation results considered in the context of ieee 802 11n show that the 2 2 mimo perfect code i e the golden code performs relatively similarly as the sdm scheme in the presence of a good outer code

channel coding with multilevel phase signals a coding technique is described which improves error performance of synchronous data links without sacrificing data rate or requiring more bandwidth this is achieved by channel coding with expanded sets of multilevel phase signals in a manner which increases free euclidean distance soft maximum likelihood ml decoding using the viterbi algorithm is assumed following a discussion of channel capacity simple hand designed trellis codes are presented for 8 phase shift keying psk and 16 quadrature amplitude shift keying qask modulation these simple codes achieve coding gains in the order of 3 4 db it is then shown that the codes can be interpreted as binary convolutional codes with a mapping of coded bits into channel signals which we call mapping by set partitioning based on a new distance measure between binary code sequences which efficiently lower bounds the euclidean distance between the corresponding channel signal sequences a search procedure for more powerful codes is developed codes with coding gains up to 6 db are obtained for a variety of multilevel phase modulation schemes simulation results are presented and an example of carrier phase tracking is discussed

infinite series representations of the bivariate rayleigh and nakagami m distributions despite the usefulness of the bivariate correlated nakagami m cumulative distribution function cdf in communications systems analysis an infinite series for the computation of this function is not known in this letter an infinite series representation of the bivariate cdf is derived bounds on the error resulting from truncation of the infinite series are also derived

asymptotic analysis and tight performance bounds of diversity receptions over beckmann fading channels with arbitrary correlation prior results on exact error rates and outage probabilities of diversity receptions over arbitrarily correlated fading channels involve intractable nested integrals which makes the performance analyses challenging to carry out in this paper we derive asymptotic expressions and asymptotically tight bounds for error rates and outage probabilities of diversity receptions including maximal ratio combining selection combining and equal gain combining over arbitrarily correlated beckmann fading channels these new asymptotic performance expressions reveal insights into the diversity systems over arbitrarily correlated beckmann fading channels and the accuracy of the asymptotic performance expressions is explicitly quantified by the performance bounds using these analytical tools one can assess the performance of the diversity reception systems over arbitrarily correlated beckmann fading channels without resorting to time consuming monte carlo simulation or numerical multifold integration

evaluating the performance of convolutional codes over block fading channels this correspondence considers union upper bound techniques for error control codes with limited interleaving over block fading rician channels a modified bounding technique is presented that relies on limiting the conditional union bound before averaging over the fading process this technique although analytically not very attractive provides tight and hence useful numerical results

some new twists to problems involving the gaussian probability integral using an alternate form of the gaussian probability integral discovered a number of years ago it is shown that the solution to a number of previously considered communication problems can be simplified and in some cases made more accurate i e exact rather than bounded these problems include the evaluation of 1 the bit error probability of uncoded phase shift keying psk with costas loop tracking 2 word error probability of antipodal modulation in the presence of fading 3 bit error probability of coded m ary psk mpsk over the memoryless fading channel with given channel state information 4 conditional symbol error probability of mpsk in the presence of carrier synchronization error and 5 the average error probability for the binary additive white gaussian noise awgn intersymbol interference channel also obtained is a generalization of this new alternate form to the case of a two dimensional gaussian probability integral with arbitrary correlation which can be used to evaluate the symbol error probability of mpsk with i q unbalance

asymptotic error analysis of diversity schemes on arbitrarily correlated rayleigh channels asymptotic error rate expressions are derived for multi branch equal gain combining and selection combining operating on arbitrarily correlated rayleigh fading channels these closed form solutions are used to provide rapid and accurate estimation of the error rates in large signal to noise ratio regions more importantly they reveal additional insights into the transmission characteristics of linear diversity combining schemes operating on correlated rayleigh fading channels it is shown that the asymptotic error rates over correlated branches can be obtained by scaling the asymptotic error rates over independent branches with a factor det m where det m is the determinant of the normalized channel correlation matrix this relationship is valid for both coherent and noncoherent signalings a similar relationship is also established for the outage probabilities of fading wireless systems employing multi branch diversity reception

invariant exponential models applied to reliability theory and survival analysis abstract for a two parameter exponential model with increasing failure rate ifr or decreasing failure rate dfr distributions necessary and sufficient conditions of the existence of a solution of the likelihood equations are given also all of the scale invariant two parameter statistical models closed by raising to a power and by exponential tilting are introduced the conditions of existence of a solution of the likelihood equations are studied for these invariant models and the models are applied to obtain some uniformly most powerful unbiased tests of exponentially against alternatives in these models

estimating shannon and constrained capacities of bernoulli gaussian impulsive noise channels in rayleigh fading this paper presents a novel approach to tightly estimate the ergodic shannon and constrained capacities of an additive bernoulli gaussian bg impulsive noise channel in rayleigh fading environments where channel gains are known at the receiver but not at the transmitter we first show that the differential entropy of the bg impulsive noise can be established in closed form using gaussian hypergeometric function 2 f 1 1 1 cdot cdot the shannon capacity is then calculated via upper and lower bounds specifically we derive in closed form two upper bounds on the shannon capacity using the assumption of a gaussian output and using full knowledge of noise state respectively under the assumption of a gaussian input we propose a novel approach to calculate a lower bound by examining the instantaneous output entropy in two regions of channel gains in the high gain region the lower bound is evaluated via the upper bound obtained under the gaussian output assumption in the other region we apply the piecewise linear curve fitting pwlcf method to estimate the lower bound it is then demonstrated that the lower bound can be calculated with a predetermined accuracy by establishing the difference between the lower bound and the two upper bounds we show that the lower bound can be used to effectively estimate the shannon capacity finally we detail a pwlcf based method to estimate the constrained capacity for a finite alphabet constellation to this end we first propose a numerical technique to calculate the instantaneous entropy of the output using 2 dimensional 2 d gauss hermite quadrature formulas the average output entropy is then obtained using the pwlcf method combined with the closed form expression of the entropy of the bg impulsive noise the constrained capacity can be effectively estimated

test of homogeneity of binary data with explanatory variables summary apparent heterogeneity of the risk of a disease in different groups may be explained by subjectspecific risk factors unequally distributed in these groups we propose a score test of homogeneity that allows adjustment for known risk factors of the disease the test is based oni a random effect logistic regression model and requires only simple computations in addition to a conventional logistic regression method the score test is applied to the study of geographical heterogeneity of cognitive impairment in elderly using a sample of 3 318 subjects scattered in 75 parishes it is shown that an apparent heterogeneity disappears when taking into account subject specific risk factors this test may also be useful for studying familial aggregation of a disease testing homogeneity of the distribution of binary traits in different groups has long been recognized as an important problem particularly in conventional genetics smith 1951 and in genetic epidemiology where it may be used to investigate the familial aggregation of a disease the presence of familial aggregation suggests a genetic determinant testing homogeneity of geographical units is also of interest the presence of heterogeneity suggests the presence of an unmeasured environmental factor another application occurs if the possible correlation of the data is treated as a nuisance it is useful to test whether the groups are homogeneous before performing ordinary regression models liang 1987 chi squared tests are used for testing homogeneity when the number of groups is small however the chi squared test is not applicable when the sizes of the groups are not large haldane 1940 and when the number of groups is large in such cases random effect models are preferred the probability of disease within a group have a common distribution thus the null hypothesis is specified by a null variance of the random effect and alternative hypotheses are specified by a unique parameter the variance of the random effect whatever the number of groups see potthoff and whittinghill 1966 wisniewsky 1968 and tarone 1979 in epidemiologic studies however we often need to test for homogeneity while adjusting for other risk factors of the disease indeed risk factors if differently distributed in the different groups may play the role of confounding factors relative to the group effect it is of paramount importance in genetic studies to investigate whether an apparent familial aggregation may be explained by nongenetic factors such as educational level or nutritional habits which may also segregate in families similarly geographical clusters may be explained by nonenvironmental factors unequally distributed in the geographical units based on a random effect logistic regression model we derive a score test of homogeneity that allows adjustment on explanatory variables the score statistic is the same as that proposed by hamerle 1990 in the context of repeated measurements but the variance proposed in the present paper is different simulations show that it leads to a more powerful test we use this test to investigate the possible geographical heterogeneity of cognitive impairment as measured by the mini mental state score in 3 318 subjects scattered in 75 parishes in southwestern france

feasibility study on the least square method for fitting non gaussian noise data abstract this study is to investigate the feasibility of least square method in fitting non gaussian noise data we add different levels of the two typical non gaussian noises levy and stretched gaussian noises to exact value of the selected functions including linear equations polynomial and exponential equations and the maximum absolute and the mean square errors are calculated for the different cases levy and stretched gaussian distributions have many applications in fractional and fractal calculus it is observed that the non gaussian noises are less accurately fitted than the gaussian noise but the stretched gaussian cases appear to perform better than the levy noise cases it is stressed that the least squares method is inapplicable to the non gaussian noise cases when the noise level is larger than 5

an analytical approach for performance evaluation of bicm transmission over nakagami m fading channels bit interleaved coded modulation bicm has established itself as a quasi standard for bandwidth and power efficient wireless communication in this paper we present an analytical approach to evaluate the performance of bicm transmission over frequency flat fading additive white gaussian noise channels the statistic of the fading envelope is modeled as nakagami m distributed which spans a wide range of practical multipath fading scenarios through adjustment of the m parameter for this setup we derive approximations for the bit error rate ber and cutoff rate of bicm different from previously proposed methods our analysis is valid for general quadrature amplitude modulation and phase shift keying signal constellations and arbitrary bit to symbol mapping rules and it results in simple closed form expressions the key idea is to use well chosen subsets of signal points to approximate the probability density function of reliability metrics used for decoding this approximation is accurate for signal to noise ratio regions of interest for bicm systems with moderate coding complexity such as e g convolutional coded bicm systems based on this approximation we also derive an asymptotic ber expression which reveals the diversity order and coding gain of bicm the usefulness of the proposed analytical approach is validated through numerical and simulation results for a number of bicm transmission examples