an optimal training signal structure for frequency offset estimation this paper addresses an optimal training signal design for frequency offset estimation based on minimizing the cramer rao lower bound for frequency offset estimation with constraints on the peak and the total training signal energies and the training block length the optimal training signal structure is developed an approximate version of the optimal training signal structure is proposed which has practically the same performance as the optimal one and provides convenience in training signal generation and estimator derivation two robust reduced complexity frequency offset estimation methods for the proposed training structures are presented in order to handle larger frequency offsets modified training signal structures are proposed frequency offset estimation methods suitable for these training signals are also derived based on the best linear unbiased estimation principle analytical and simulation results show that the proposed training signal structures improve the estimation performance significantly

maximum likelihood based estimation of frequency and phase offset in dct ofdm systems under non circular transmissions algorithms analysis and comparisons recently the advantages of the discrete cosine transform dct based orthogonal frequency division multiplexing ofdm have come to the light we thus consider dct ofdm with non circular transmission our results cover circular transmission as well and present two blind joint maximum likelihood frequency offset and phase offset estimators both our theoretical analysis and numerical comparisons reveal new advantages of dct ofdm over the traditional discrete fourier transform dft based ofdm these advantages as well as those already uncovered in the early works on dct ofdm support the belief that dct ofdm is a promising multi carrier modulation scheme

a reduced complexity channel estimation for ofdm systems with transmit diversity in mobile wireless channels a reduced complexity channel estimation for ofdm systems with transmit diversity is proposed by exploiting the correlation of the adjacent subchannel responses the sizes of the matrix inverse and the ffts required in the channel estimation at every ofdm data symbol are reduced by half of the existing method for ofdm systems with nonconstant modulus subcarrier symbols or constant modulus subcarrier symbols with some guard tones the complexity reduction of half ffts size and some matrix multiplications is still achieved for constant modulus subcarrier symbols with no guard tones the price for the complexity reduction is a slight ber degradation and for the channels with small relative delay spreads the ber performance of the reduced complexity method becomes quite comparable to the existing method an alternative approach for the number of significant taps required in the channel estimation is described which achieves a comparable performance to the case with the known suitable number of significant taps a simple modification which reduces the lost leakage of the nonsample spaced channel paths is also proposed this modification achieves a substantial performance improvement over the existing method without any added complexity

single carrier systems with mmse linear equalizers performance degradation due to channel and cfo estimation errors we assess the impact of the channel and the carrier frequency offset cfo estimation errors on the performance of single carrier systems with mmse linear equalizers performance degradation is caused by the fact that a mismatched mmse linear equalizer is applied to channel output samples with imperfectly canceled cfo assuming a single block training we develop an asymptotic expression for the excess mean square error emse induced by the channel and cfo estimation errors and derive a simple emse approximation which reveals the following 1 performance degradation is mainly caused by the imperfectly canceled cfo and 2 the emse is approximately proportional to the cfo estimation error variance with the factor of proportionality being independent of the training sequence we also highlight the fact that the placement of the single block training at the middle of the packet is a good practice

adaptive ofdm synchronization algorithms based on discrete stochastic approximation this paper presents discrete stochastic approximation algorithms dsa for time synchronization in orthogonal frequency division multiplexing ofdm systems it is shown that the discrete stochastic approximation algorithms can be effectively used to achieve a significant reduction in computational complexity compared to brute force maximum likelihood ml methods for ofdm synchronization the most important property of the proposed algorithms is their recursive self learning capability most of the computational effort is spent at the global or a local optimizer of the objective function the convergence of the algorithms is analyzed an adaptive version of the discrete stochastic approximation algorithm is also presented for tracking time varying time delays and frequency offsets in time selective fading channels detailed numerical examples illustrate the performance gains of these dsa based synchronization algorithms

an efficient carrier phase synchronization technique for high order m qam ofdm in this correspondence we propose a blind carrier phase synchronization algorithm for high order m ary quadrature amplitude modulation orthogonal frequency division multiplexing m qam ofdm systems which can effectively recover residual frequency offset rfo in the presence of intercarrier interference ici the proposed algorithm performs frequency and phase synchronization by using post fast fourier transform fft demodulated signals without the aid of reference signals e g pilots guard intervals and virtual carriers and is simple to implement by analyzing its open loop characteristics we show that the proposed algorithm is superior to the conventional decision directed dd scheme for high order m qam ofdm systems

approachability and fixed points for non convex set valued maps this paper studies the approachability of upper semicontinuous nonconvex set valued maps by single valued continuous functions and its applications to fixed point theory the use of approximate selections was initiated by j von neumann 41 in the proof of his well known minimax principle this remarkable property was extended to the normed space setting by cellina s and cellina and lasota 9 in the context of a degree theory for upper semicontinuous convex compact valued maps it also holds for maps with compact contractible values defined on finite polyhedra of iw ma cole11 40 and more generally defined on compact anrs mclennan 39 it was recently taken up by gbrniewicz granas and kryszewski 22 241 in the context of an index theory for non convex maps defined on compact anrs the content of this paper is divided into three parts the first part is devoted to background material concerning the types of spaces and set valued maps studied herein in the second part we define the abstract class d of approachable set valued maps that is the class of maps a x y

synchronization requirements for multi user ofdm on satellite mobile and two path rayleigh fading channels the performance of multi user orthogonal frequency division multiplexing ofdm with raised cosine time domain pulse shaping is studied on the satellite mobile channel smc and the two path rayleigh fading channel a multi user time and carrier frequency synchronization scheme is discussed the relationship between the synchronization requirement and the roll off rate spl beta of the pulse shaping is explored in gaussian and typical rician k 10 channels multi user ofdm with spl beta 0 2 requires timing and carrier frequency synchronization accuracies of 4 and 2 respectively in order to avoid severe degradation due to multi user adjacent channel interference while on the two path rayleigh channel these values must be better than 2 for error floors less than 10 sup 3 timing and carrier frequency accuracies are normalized to t and 1 t respectively where t is the symbol duration multi user ofdm is less affected by the multipath time delay and slightly more severely affected by the doppler frequency shift than traditional fdm with root nyquist filtering fdm rnf for the same value of spl beta

a statistical inter cell interference model for downlink cellular ofdma networks under log normal shadowing and multipath rayleigh fading the probability density function pdf of the intercell interference for downlink cellular orthogonal frequency division multiple access networks under log normal shadowing and multipath rayleigh fading is derived the derived pdf is observed to highly deviate from the gaussian distribution especially at moderate to small network loads based on the derived inter cell interference statistics the decoder performance can be significantly improved compared to the case when the traditional decoder optimized for the awgn channel is employed a simple suboptimum decoding algorithm that closely approximates the derived optimum decoder performance is also proposed

maximum likelihood detection for differential unitary space time modulation with carrier frequency offset can conventional differential unitary space time modulation dustm be applied when there is an unknown carrier frequency offset cfo this paper answers this question affirmatively and derives the necessary maximum likelihood ml detection rule the asymptotic performance of the proposed ml rule is analyzed leading to a code design criterion for dustm by using the modified diversity product the resulting proposed decision rule is a new differential modulation scheme in both the temporal and spatial domains two sub optimal multiple symbol decision rules with improved performance are also proposed for the efficient implementation of these we derive a modified bound intersection detector bid a generalization of the previously derived optimal bid for the conventional dustm the simulation results show that the proposed differential modulation scheme is more robust against cfo drifting than the existing double temporal differential modulation

the effect of diversity on a burst mode carrier frequency estimator in the frequency selective multipath channel this paper describes a carrier frequency offset estimator derived using maximum likelihood techniques the estimator is designed for a digital space diversity receiver operating in a wide band frequency selective multipath fading channel the estimator is suited to a burst mode time division multiple access system because the estimate is formed in an open loop manner and relies on a training sequence normally used in burst mode systems the main advantage is that it does not require channel state information rather it only requires knowledge of the auto correlation of the channel simulation results show the estimator to be unbiased over a wide frequency range the normalized error standard deviation is shown to be 0 0015 across the frequency offset range for a receiver with four diversity branches when the normalized channel delay spread is 0 1 the signal to noise ratio snr is 10 db and the training sequence length is 23 symbols it is found that for most parameter configurations there is approximately a factor of two improvement in the estimate error standard deviation when the antenna diversity is doubled

lmse based parameter acquisition for multicarrier cdma systems an acquisition scheme based on the least mean squared error lmse for the symbol timing carrier phases and multipath gains for multicarrier code division multiple access mc cdma systems is proposed a new coefficient called the quasi mean squared accuracy coefficient qmsac is introduced this allows the search for multiple optimal parameters to be split into simpler single parameter estimates the symbol timing is acquired with a comparison of the qmsacs followed by a linear interpolation scheme or a search of a minimizing variable carrier phases and multipath gain coefficients are then estimated via some algebraic computations based only on the estimated symbol timing and the qmsacs the spreading sequence of the desired user is the only prior knowledge required for the proposed approach simulation results demonstrate the near far resistance of the approach and show that the error performance of minimum mean squared error mmse detection with acquired parameters is only a few decibels worse for the considered channel than the performance obtained with perfect knowledge about the channel impulse response

multi scale multi lag channel estimation using low rank approximation for ofdm this paper considers the estimation of multi scale multi lag msml channels the msml channel model is a good representation for wideband communication channels such as underwater acoustic communication and radar this model is characterized by a limited number of paths each parameterized by a delay doppler scale and attenuation factor herein it is shown that an ofdm signal after passing through the msml channel exhibits a low rank representation this feature can be exploited to improve the channel estimation by characterizing the received signal it is shown that the msml channel estimation problem can be adapted to a structured spectral estimation problem the challenge is that the unknown frequencies are very close to each other due to the small values of doppler scales this feature can be employed to show that the data matrix is approximately low rank by exploiting structural features of the received signal the prony algorithm is modified to estimate the doppler scales close frequencies delays and channel gains two strategies using convex and no convex regularizers to remove noise from the corrupted signal are proposed these algorithms are iterative based on the alternating direction method of multipliers a bound on the reconstruction of the noiseless received signal provides guidance on the selection of the relaxation parameter in the optimizations the performance of the proposed estimation strategies are investigated via numerical simulations and it is shown that the proposed non convex method offers up to 7 db improvement in low snr and the convex method offers up to 5 db improvement in high snr over prior methods for the msml channel estimation

fractional equations and generalizations of schaefer s and krasnoselskii s fixed point theorems abstract we study a fractional differential equation of caputo type by first transforming it into an integral equation with an l 1 0 kernel and then applying fixed point theory of banach and schauder type using a weighted norm to avoid stringent compactness conditions it becomes clear that tedious construction of mapping sets and boundedness conditions can be avoided if we use fixed point theorems of schaefer and krasnoselskii type the weighted norm then produces open sets so large that it is difficult to show that mappings are compact this then leads us to generalize both schaefer s and krasnoselskii s fixed point theorems which yield simple and direct qualitative results for the fractional differential equations the weight g yields compactness but it does much more the generalized fixed point theorems now yield growth properties of the solutions of the fractional differential equations

autocorrelation based decentralized sequential detection of ofdm signals in cognitive radios this paper introduces a simple and computationally efficient spectrum sensing scheme for orthogonal frequency division multiplexing ofdm based primary user signal using its autocorrelation coefficient further it is shown that the log likelihood ratio test llrt statistic is the maximum likelihood estimate of the autocorrelation coefficient in the low signal to noise ratio snr regime performance of the local detector is studied for the additive white gaussian noise awgn and multipath channels using theoretical analysis obtained results are verified in simulation the performance of the local detector in the face of shadowing is studied by simulations a sequential detection sd scheme where many secondary users cooperate to detect the same primary user is proposed user cooperation provides diversity gains as well as facilitates using simpler local detectors the sequential detection reduces the delay and the amount of data needed in identification of the underutilized spectrum the decision statistics from individual detectors are combined at the fusion center fc the statistical properties of the decision statistics are established the performance of the scheme is studied through theory and validated by simulations a comparison of the sd scheme with the neyman pearson fixed sample size fss test for the same false alarm and missed detection probabilities is also carried out

fixed point theory for admissible multimaps defined on closed subsets of frechet spaces abstract this paper presents new fixed point results for a general class of maps defined on frechet spaces our results in particular apply to kakutani acyclic o neill approximable admissible with respect to gorniewicz and u c maps

fixed points for better admissible multifunctions on proximity spaces abstract we set out a rigorous presentation of park s classes of admissible multifunctions and we obtain a fixed point theorem for better admissible multifunctions defined on a proximity space via the samuel smirnov compactification

on the distribution of the length of the longest increasing subsequence of random permutations let sn be the group of permutations of 1 2 n if 7r e sn we say that 7 i1 7f ik is an increasing subsequence in 7r if il i2 ik and 7r ii 7r i2 7r ik let 1n r be the length of the longest increasing subsequence for example if n 5 and 7r is the permutation 5 1 3 2 4 in one line notation thus 7r 1 5 7r 2 1 then the longest increasing subsequences are 1 2 4 and 1 3 4 and n 3 equip sn with uniform distribution

fixed point theorems for multifunctions having kkm property on almost convex sets in this paper for two nonempty subsets x and y of a linear space e we define the class kkm x y and investigate the fixed point problem for t kkm x x with x an almost convex subset of a locally convex space our fixed point theorem contains lassonde fixed point theorem for kakutani factorizable multifunctions as special case

exact and approximate construction of digital phase modulations by superposition of amplitude modulated pulses amp minimum shift keying and offset qpsk are two well known modulations which can be interpreted as a set of time phase shifted am pulses we show in this paper that any constant amplitude binary phase modulation can also be expressed as a sum of a finite number of time limited amplitude modulated pulses amp decomposition new methods for computing autocorrelation and power frequency spectrum are derived which give very simple results for half integer index modulations we also show that the signal can be built with good accuracy using only one optimized pulse main pulse this synthesis is particularly satisfactory for modulations that have good spectral characteristics and or low index

maximum likelihood synchronization and channel estimation for ofdma uplink transmissions maximum likelihood estimation of the carrier frequency offset cfo timing error and channel response of each active user in the uplink of an orthogonal frequency division multiple access system is investigated in this study assuming that a training sequence is available the exact solution to this problem turns out to be too complex for practical purposes as it involves a search over a multidimensional domain however making use of the alternating projection method we replace the above search with a sequence of mono dimensional searches this results in an estimation algorithm of a reasonable complexity which is suitable for practical applications as compared with other existing semi blind methods the proposed algorithm requires increased overhead but has more flexibility as it can be used with any subcarrier assignment scheme simulations indicate that the accuracy of the cfo estimates asymptotically achieves the cramer rao bound

blind symbol timing and frequency offset estimation in ofdm systems with real data symbols in this letter the problem of blind symbol timing and frequency offset estimation in orthogonal frequency division multiplexing ofdm systems with real data symbols is considered maximum likelihood ml estimators for the parameters of interest have been derived by modeling the ofdm signal as a proper complex gaussian random process however when data symbols belong to a real constellation the received signal becomes an improper complex random process and hence previously mentioned estimators termed cyclic prefix cp estimators are not ml estimators in this letter minimum mean squared error estimators exploiting the conjugate symmetry property exhibited by the ofdm signal with real data symbols termed msr estimators that greatly outperform cp estimators in additive noise channels are derived moreover a modified msr symbol timing estimator that can assure satisfactory performance in multipath fading channels is proposed

remark on krasnoselskii s fixed point theorem abstract a well known result due to krasnoselskii ensures the existence of a fixed point for an operator k a b which is defined on a non empty bounded closed convex subset s of a banach space x where i a is a contraction ii b is a compact operator and iii a s b s s in the present note an easy sufficient condition for fulfilling iii in the case of a locally convex space is given an application to the existence of solutions of a nonlinear integral equation illustrates this result

non redundant precoding based blind and semi blind channel estimation for mimo block transmission with a cyclic prefix by combining multiple input multiple output mimo communication with block transmission using a cyclic prefix cp mimo block transmission systems can not only achieve high data rates but also simplify channel estimation and equalization in this paper to provide a bandwidth efficient solution for channel estimation in mimo block transmission systems with a cp we present a framework for blind channel estimation based on a general non redundant precoding using this framework we propose a blind estimator exploiting a simplified non redundant precoding that is robust against overestimates of a true mimo channel order furthermore in the case with the number of transmit antennas greater than that of receive antennas we show under specific system conditions that the proposed blind algorithms can be used for estimation of the mimo channel without oversampling the received signals with the simplified precoding conditions established in this paper the proposed method does not impose the strict identifiability conditions on the mimo channel which are required for the existing methods furthermore the proposed estimator achieves accurate channel estimation with a small number of symbol blocks in addition we derive a simplified precoder that is optimized in the sense of minimizing the impact of unknown additive noise we discuss the tradeoff between channel estimation accuracy and bit error rate performance associated with the simplified precoder finally we develop a technique for resolving the channel ambiguity in the proposed blind estimator to create a semi blind channel estimator relying on only a few known symbols

a unification theory of krasnoselskii for differential equations abstract the theory of differential equations is very broad and contains many seemingly unrelated types of problems with markedly different methods of solution it is very difficult to discern any unity in the theory yet sixty years ago one of the foremost investigators krasnoselskii suggested the possibility of finding unity he claimed that the inversion of a perturbed differential operator yields the sum of a contraction and compact map accordingly he proved a general fixed point theorem to cover this situation in this paper we begin a long study with a view to putting his idea to the test we begin with fractional differential equations of caputo type continue to neutral functional differential equations and conclude with a study of an old problem of volterra which continues to describe many important real world problems for these problems there is the perfect unity predicted by krasnoselskii it is an invitation to continue the study by examining other important real world problems

analysis of aeroplane boarding via spacetime geometry and random matrix theory we show that aeroplane boarding can be asymptotically modelled by two dimensional lorentzian geometry boarding time is given by the maximal proper time among curves in the model discrepancies between the model and simulation results are closely related to random matrix theory the models can be used to explain why some commonly practised airline boarding policies are ineffective and even detrimental

symbol time offset estimation in coherent ofdm systems this paper presents a symbol time offset estimator for coherent orthogonal frequency division multiplexing ofdm systems the estimator exploits both the redundancy in the cyclic prefix and available pilot symbols used for channel estimation the estimator is robust against frequency offsets and is suitable for use in dispersive channels we base the estimator on the maximum likelihood estimator for the additive white gaussian noise channel simulations for an example system indicate a system performance as close as 0 6 db to a perfectly synchronized system

low complexity residual doppler shift estimation for underwater acoustic multicarrier communication we propose two computationally efficient residual doppler shift estimation methods for underwater acoustic multicarrier communication the first method is based on computing the phase of the root of a low order polynomial the second method is a closed form least squares estimate given the unwrapped phases of the minimal eigenvector of a small data matrix the complexities of both estimates are significantly lower compared to the methods commonly used in underwater acoustic multicarrier communication which result in nonlinear least squares estimators and thus require a fine grid search in the frequency domain numerical simulations show that the mean square errors of the proposed methods have similar performance as the common estimation techniques achieve the cramer rao lower bounds at low noise levels and agree with their theoretically derived variances pool experiments and sea trial results further demonstrate that the suggested estimates yield similar results as the common nonlinear least squares estimates but at a lower complexity

on the approximation of upper semi continuous correspondences and the equilibriums of generalized games in section 1 we explain some of the definitions and terminology that we use in section 2 we prove several theorems concerning the approximation of upper semi continuous correspondences having for range a locally convex space theorems 1 and 2 and corollary 1 generalize certain approximation theorems by g haddad 16 pp 1352213541 g haddad and j m lasry 17 pp 299 3001 and j p aubin and a cellina 2 pp 86891 see also f s de blasi lo and j m lasry and r robert 21 although some of the details of the proofs of theorems 1 and 2 are new the basic ideas are taken from the above mentioned papers theorem 3 shows that the correspondences in the approximating families can be chosen so that they are regular see section 1 this theorem see the remark following its proof contains a classical result of m hukuhara 18 pp 56573 theorem 3 is proved using theorem 2 and propositions 1 and 4 variants of propositions 2 3 and 4 were given in 193 in section 3 we give among others theorem 5 which concerns the existence of equilibriums of generalized games abstract economies the main purpose of this result is to replace the continuity hypothesis in the w shafer h sonnenschein equilibrium theorem for generalized games by an upper semi continuity one the proof of theorem 5 is based on the results on the approximation of upper semi continuous correspondences obtained in section 2 theorem 5 us used in section 4 in section 4 we establish theorems 6 and 7 these theorems show that certain statements concerning the equilibrium of generalized games are equivalent to certain statements concerning minimax inequalities of k fan type theorems 1 2 3 5 6 and 7 are the main results of this paper 267 0022 247x 88 3 00

a simple interpolation technique for the dft for joint system parameters estimation in burst mpsk transmissions in this paper we propose a simple frequency domain interpolation technique for the discrete fourier transform dft this interpolation technique can significantly improve the frequency and phase resolution capabilities of the dft without increasing the size of the dft the number of points used for the dft this new technique employs a dividing point in the amplitude and phase spectra suitable areas of application include joint estimation of fine frequency and phase offsets in burst mode digital transmission

probability of error analysis of bpsk ofdm systems with random residual frequency offset in this paper we derive closed form bit error rate ber expressions for orthogonal frequency division multiplexing ofdm systems with residual carrier frequency offset cfo most of the published work treats cfo as a nonrandom parameter but in our study we consider it as a random parameter the ber performance of binary phase shift keying bpsk ofdm system is analyzed in the cases of additive white gaussian noise awgn frequency flat and frequency selective rayleigh fading channels we further discuss how these expressions can be related to systems with practical estimators the simulation results are provided to verify the accuracy of these error rate expressions

carrier frequency offset estimation for ofdm systems using null subcarriers carrier frequency offset cfo in orthogonal frequency division multiplexing ofdm systems which can induce the loss of orthogonality among subcarriersand result in significant performance degradation is critical to be estimatedand compensated for in this paper a suboptimal scheme is proposed to estimatethe cfo using null subcarriers in the proposed scheme the cfo is dividedinto the fractional part and the integer part with the fractional cfo estimatedfollowed by the integer cfo estimation compared with previous work usingnull subcarriers and exhaustive search the implementation complexity of theproposed scheme is significantly lower due to the fact that the main componentrequired is a simple correlator furthermore with only one trainingofdm symbol and proper null subcarrier allocation the estimation range ofthe proposed scheme can be the inverse of the sampling duration in contrast conventional schemes with the same estimation range and complexity require two ofdm symbols to achieve good performance it will be shown that the null subcarrier allocation should be based uponsome specific binary sequences such as the proposed extended m sequences it willalso be shown by simulations that the same null subcarrier allocation criterionshould be employed for optimal maximum likelihood cfo estimation

blind frequency synchronization in ofdm via diagonality criterion in this paper we address the problem of blind carrier frequency offset cfo estimation in orthogonal frequency division multiplexing ofdm systems in the case of frequency selective channels cfo destroys the orthogonality between the carriers leading to nondiagonal signal covariance matrices in frequency domain the proposed blind method enforces a diagonal structure by minimizing the power of nondiagonal elements hence the orthogonality property inherent to ofdm transmission with cyclic prefix is restored the method is blind since it does not require a priori knowledge of the transmitted data or the channel and does not need any virtual subcarriers a closed form solution is derived which leads to accurate and computationally efficient cfo estimation in multipath fading environments consistency of the estimator is proved and the convergence rate as a function of the sample size is analyzed as well to assess the large sample performance we derive the cramer rao bound crb for the blind cfo estimation problem the crb is derived assuming a general gaussian model for the ofdm signal which may be applied to both circular and noncircular modulations finally simulation results on cfo estimation are reported using a realistic channel model

fine frequency synchronization in the uplink of multiuser ofdm systems this contribution considers the estimation and compensation of residual multiple carrier frequency offsets cfos and sampling frequency offsets sfos in the uplink of multiuser ofdm systems based on the observation of a user dependent phase rotation an approximate maximum likelihood ml estimator is proposed in order to estimate the cfos and sfos and to track the phase in a post synchronization step by using a taylor approximation the estimation complexity is reduced bit error ratio ber simulations show that the system performance degradation due to small frequency mismatches is negligible if the proposed method is applied

optimal sequences for channel estimation using discrete fourier transform techniques this paper addresses the problem of selecting the optimum training sequence for channel estimation in communication systems over time dispersive channels by processing in the frequency domain a new explicit form of search criterion is found the gain loss factor glf which minimizes the variance of the estimation error and is easy to compute theoretical upper and lower bounds on the glf are derived an efficient directed search strategy and optimal sequences up to length 42 are given these sequences are optimal only for frequency domain estimation not for time domain estimation

krasnoselskii s fixed point theorem for weakly continuous maps abstract we consider the sum a b m x where m is a weakly compact and convex subset of a banach space x a m x is weakly continuous and b l x with bp 1 p 1 an alternative condition is given in order to guarantee the existence of fixed points in m for a b some illustrative applications are given

limit laws for the asymmetric inclusion process the asymmetric inclusion process asip is a unidirectional lattice gas flow model which was recently introduced as an exactly solvable bosonic counterpart of the fermionic asymmetric exclusion process an iterative algorithm that allows the computation of the probability generating function pgf of the asip s steady state exists but practical considerations limit its applicability to small asip lattices large lattices on the other hand have been studied primarily via monte carlo simulations and were shown to display a wide spectrum of intriguing statistical phenomena in this paper we bypass the need for direct computation of the pgf and explore the asip s asymptotic statistical behavior we consider three different limiting regimes heavy traffic regime large system regime and balanced system regime in each of these regimes we obtain analytically and in closed form stochastic limit laws for five key asip observables traversal time overall load busy period first occupied site and draining time the results obtained yield a detailed limit laws perspective of the asip numerical simulations demonstrate the applicability of these laws as useful approximations

occupation probabilities and fluctuations in the asymmetric simple inclusion process the asymmetric simple inclusion process asip a lattice gas model of unidirectional transport and aggregation was recently proposed as an inclusion counterpart of the asymmetric simple exclusion process in this paper we present an exact closed form expression for the probability that a given number of particles occupies a given set of consecutive lattice sites our results are expressed in terms of the entries of catalan s trapezoids number arrays which generalize catalan s numbers and catalan s triangle we further prove that the asip is asymptotically governed by the following i an inverse square root law of occupation ii a square root law of fluctuation and iii a rayleigh law for the distribution of interexit times the universality of these results is discussed

some results for the family kkm x y and the φ mapping abstract in this paper we first establish a fixed point theorem for a k set contraction map on the family kkm x x which not needs to be a compact map next we establish the matching theorems coincidence theorems and minimax theorems on the family kkm x y and the mapping

comments on class of cyclic based estimators for frequency offset estimation of ofdm systems this comment corrects several errors found in the paper class of cyclic based estimators for frequency offset estimation of ofdm systems in addition we show that the minimum variance unbiased estimator for frequency offset derived in the above paper is the maximum likelihood estimator when the timing delay is perfectly known

pilot designs for consistent frequency offset estimation in ofdm systems this paper presents pilot designs for consistent frequency offset estimation of orthogonal frequency division multiplexing systems in frequency selective fading channels we describe two design approaches namely consistency in the probabilistic sense and absolute consistency existing preambles and pilot designs in the literature do not guarantee the absolute consistency we derive general criteria for both approaches present sufficient conditions on the pilot structures over the maximum carrier frequency offset cfo estimation range half of the sampling rate and derive simple pilot designs satisfying these conditions we also extend the sufficient conditions to any arbitrary but fixed cfo estimation range and present some generalized design patterns furthermore the cfo estimation performances of distinct consistent pilot designs can be quite different at moderate or low signal to noise ratio snr due to different statistics of outliers which also yields a link failure we develop efficient pilot design criteria that provide both consistency and robustness against outliers at moderate to low snr our consistent pilot designs facilitate flexible and economical implementation while our robust pilot designs enable wireless links with less outage and better resilience

numerically stable and efficient algorithm for vector channel parameter and frequency offset estimation in this paper we present a novel and numerically efficient algorithm for vector channel and calibration vector estimation which works when frequency offset error caused by either unstable oscillator or doppler effect is present in spread spectrum antenna system we propose an estimation algorithm based on gauss seidal algorithm rather than using eigen decomposition or svd in computing eigenvalues and eigenvectors at each iteration the algorithm is based on the two step procedures one for estimating both channel and frequency offset and the other for estimating the unknown array gain and phase consequently estimates of the doas the multi path impulse response of the reference signal source and the carrier frequency offset as well as the calibration of antenna array are provided the analytic performance improvement in multiplications number is presented the performance of the proposed algorithm is investigated by means of computer simulations throughout the analytic and computer simulation we show that the proposed algorithm reduces the number of multiplications by order of one

generalizations of the krasnoselskii fixed point theorem abstract we obtain new generalized forms of the krasnoselskii theorem on fixed points for a sum of two operators and show that our new results encompass a number of previously known generalizations of the theorem

coincidence theory for multimaps abstract several continuation principles in a variety of settings are presented which guarantee the existence of coincidence points for a general class of multimaps

exploiting input cyclostationarity for blind channel identification in ofdm systems transmitter induced cyclostationarity has been explored previously as an alternative to fractional sampling and antenna array methods for blind identification of fir communication channels an interesting application of these ideas is in ofdm systems which induce cyclostationarity due to the cyclic prefix we develop a novel subspace approach for blind channel identification using cyclic correlations at the ofdm receiver even channels with equispaced unit circle zeros are identifiable in the presence of any nonzero length cyclic prefix with adequate block length simulations of the proposed channel estimator along with its performance in ofdm systems combined with impulse response shortening and reed solomon coding are presented

generalized multivalued quasi variational inequalities in this paper we introduce and study a new class of variational inequalities known as generalized multivalued quasi variational inequalities this class is the most general and unifying one using essentially the projection technique we establish the equivalence between this class and the implicit wiener hopf equations this equivalence is used to suggest a number of iterative algorithms for solving the generalized multivalued quasi variational inequalities the convergence analysis of these algorithms is also studied the results proved in this paper represent a significant improvement and refinement of the previously known results in this area

temporal synchronization of mimo wireless communication in the presence of interference in wireless communications systems that potentially operate in interference acquisition and temporal alignment of a transmitted signal by a receiver can be the most fragile component of the link in this paper synchronization detection in the presence of interference for multiple input multiple output mimo communication is discussed here synchronization indicates signal acquisition and timing estimation at the receiver and is formulated as a binary statistical hypothesis test transmit sequences from multiple antennas are received by multiple antennas in noisy environments with spatially correlated noise interference flat fading and frequency selective channel models for both the interference and signal of interest are considered by applying well known multiple antenna approaches to the mimo synchronization problem a number of new synchronization test statistics are introduced these test statistics are motivated by minimum mean square error mmse beamformers generalized likelihood ratio test glrt least squared ls channel estimation and spatial invariance test statistics appropriate for orthogonal frequency division multiplexing ofdm systems are considered including test statistics that take advantage of cyclic prefixes and of pilot sequences within an ofdm symbol performances of various test statistics in terms of probability of missing detection for some probability of a false detection are shown to vary by multiple orders of magnitude in the presence of interference

class of cyclic based estimators for frequency offset estimation of ofdm systems we present a new class of blind cyclic based estimators for carrier frequency offset and symbol timing error estimation of orthogonal frequency division multiplexing ofdm systems the proposed approach exploits the properties of the cyclic prefix subset to reveal the synchronization parameters in the likelihood function of the received vector a new likelihood function for the joint timing and frequency offset estimation is derived which globally characterizes the estimation problem the resulting probabilistic measure is used to develop three classes of unbiased estimators namely maximum likelihood minimum variance unbiased and moment estimator in comparison to the previously proposed methods the proposed estimators in this study are computationally and statistically efficient which makes the estimators more attractive for real time applications the performance of the estimators is assessed by simulation for an ofdm system

low complexity nonlinear least squares carrier offset estimator for ofdm identifiability diversity and performance orthogonal frequency division multiplexing ofdm transforms frequency selective channels into multiple low rate flat fading subchannels carrier frequency offset between transmitter and receiver local oscillators must be estimated and compensated at the receiver to maintain orthogonality of these subchannels in this paper we derive the nonlinear least squares nls estimator for carrier frequency synchronization that exploits receiver diversity and known ofdm signal subspace structure due to the placement of unmodulated virtual subcarriers the resulting estimator benefits from the high resolution subspace method without the computational overhead associated with subspace decomposition fundamental estimator performance relationships against parameters such as signal to noise ratio snr frequency selective fading and diversity branch correlation are derived in particular we derive the cramer rao bound crb for the mean square error mse of the carrier frequency offset estimator numerical studies are presented to verify the results

on the reduction of krasnoselskii s theorem to schauder s theorem abstract krasnoselskii noted that many problems in analysis can be formulated as a mapping which is the sum of a contraction and compact map he proved a theorem covering such cases which is the union of the contraction mapping principle and schauder s second fixed point theorem in putting the two results together he found it necessary to add a condition which has been difficult to fulfill although a great many problems have been solved using his result and there have been many generalizations and simplifications of his result in this paper we point out that when the mapping is defined by an integral plus a contraction term the integral can generate an equicontinuous map which is independent of the smoothness of the functions because of that it is possible to set up that mapping not as a sum of contraction and compact map but as a continuous map on a compact convex subset of a normed space an application of schauder s first fixed point theorem will then yield a fixed point without any reference to that difficult condition of krasnoselskii finite and infinite intervals are handled separately for the class of problems considered application is parallel to the much simpler brouwer fixed point theorem

recent results in analytical fixed point theory we survey recent results in analytical fixed point theory firstly we state resolutions of long standing problems in infinite dimensional topology the schauder conjecture the compact ar problem and the banach problem on the hilbert cube secondly we list some fixed point theorems on kakutani maps generalized upper hemicontinuous maps fan browder maps approximable maps acyclic maps and admissible or better admissible class b of maps some related results are also given

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

new blind block synchronization for transceivers using redundant precoders this paper studies the blind block synchronization problem in block transmission systems using linear redundant precoders lrp two commonly used lrp systems namely zero padding zp and cyclic prefix cp systems are considered in this paper in particular the block synchronization problem in cp systems is a broader version of timing synchronization problem in the popular orthogonal frequency division multiplexing ofdm systems the proposed algorithms exploit the rank deficiency property of the matrix composed of received blocks when the block synchronization is perfect and use a parameter called repetition index which can be chosen as any positive integer theoretical results suggest advantages in blind block synchronization performances when using a large repetition index furthermore unlike previously reported algorithms which require a large amount of received data the proposed methods with properly chosen repetition indices guarantee correct block synchronization in absence of noise using only two received blocks in zp systems and three in cp systems computer simulations are conducted to evaluate the performances of the proposed algorithms and compare them with previously reported algorithms simulation results not only verify the capability of the proposed algorithms to work with limited received data but also show significant improvements in the block synchronization error rate performance of the proposed algorithms over previously reported algorithms

asymptotically efficient reduced complexity frequency offset and channel estimators for uplink mimo ofdma systems in this paper we address the joint data aided estimation of frequency offsets and channel coefficients in uplink multiple input multiple output orthogonal frequency division multiple access mimo ofdma systems as the maximum likelihood ml estimator is impractical in this context we introduce a family of suboptimal estimators with the aim of exhibiting an attractive tradeoff between performance and complexity the estimators do not rely on a particular subcarrier assignment scheme and are thus valid for a large number of ofdma systems as far as complexity is concerned the computational cost of the proposed estimators is shown to be significantly reduced compared to existing estimators based on ml as far as performance is concerned the proposed suboptimal estimators are shown to be asymptotically efficient i e the covariance matrix of the estimation error achieves the cramer rao bound when the total number of subcarriers increases simulation results sustain our claims

algorithms and bounds for distributed tdoa based positioning using ofdm signals one main drawback of using time difference of arrival tdoa methods for source localization and navigation is that they require centralization of multiple copies of a signal this paper considers blindly estimating the location of a cyclic prefix cp in an orthogonal frequency division multiplexing ofdm signal enabling distributed tdoa computation up to an integer ambiguity this ambiguity can be resolved using integer least squares methods if enough tdoas are available requiring only minimal cooperation between receivers the contributions of this paper are development of an algorithm for simultaneously resolving the integer ambiguities and obtaining a position estimate and derivation of the cramer rao lower bound crlb on locating the cp and hence on the underlying source localization and navigation problems

carrier frequency estimation for transmissions over selective channels this paper deals with carrier frequency estimation for burst transmissions over frequency selective channels three estimation schemes are proposed all based on the use of known training sequences the first scheme employs an arbitrary sequence and provides joint maximum likelihood ml estimates of the carrier frequency and the channel response its implementation complexity is relatively high but its accuracy achieves the cramer rao bound the second scheme is still based on the ml criterion but the training sequence is periodic which helps to reduce the computational load the third scheme also employs periodic sequences but its structure comes from heuristic reasoning theoretical analysis and simulations are employed to assess the performance of the three schemes

time needed to board an airplane a power law and the structure behind it a simple model for the boarding of an airplane is studied passengers have reserved seats but enter the airplane in arbitrary order queues are formed along the aisle as some passengers have to wait to reach the seats for which they have reservation we label a passenger by the number of his or her reserved seat in most cases the boarding process is much slower than for the optimal situation where passenger and seat orders are identical we study this dynamical system by calculating the average boarding time when all permutations of n passengers are given equal weight to first order the boarding time for a given permutation ordering of the passengers is given by the number s of sequences of monotonically increasing values in the permutation we show that the distribution of s is symmetric on 1 n which leads to an average boarding time n 1 2 we have found an exact expression for s and have shown that the full distribution of s approaches a normal distribution as n increases however there are significant corrections to the first order results due to certain correlations between passenger ordering and the substrate seat ordering this occurs for some cases in which the sequence of the seats is partially mirrored in the passenger ordering these cases with correlations have a boarding time that is lower than predicted by the first order results the large number of cases with reduced boarding times have been classified we also give some indicative results on the geometry of the correlations with sorting into geometry groups with increasing n both the number of correlation types and the number of cases belonging to each type increase rapidly using enumeration we find that as a result of these correlations the average boarding time behaves like n with 0 69 as compared with 1 0 for the first order approximation

ml estimation of time and frequency offset in ofdm systems we present the joint maximum likelihood ml symbol time and carrier frequency offset estimator in orthogonal frequency division multiplexing ofdm systems redundant information contained within the cyclic prefix enables this estimation without additional pilots simulations show that the frequency estimator may be used in a tracking mode and the time estimator in an acquisition mode

a topological and geometric approach to fixed points results for sum of operators and applications abstract in this paper we establish a fixed point result of krasnoselskii type for the sum a b where a and b are continuous maps acting on locally convex spaces our results extend previous ones we apply such results to obtain strong solutions for some quasi linear elliptic equations with lack of compactness we also provide an application to the existence and regularity theory of solutions to a nonlinear integral equation modeled in a banach space in the last section we develop a sequentially weak continuity result for a class of operators acting on vector valued lebesgue spaces such a result is used together with a geometric condition as the main tool to provide an existence theory for nonlinear integral equations in l p e

a fine blind frequency offset estimator for ofdm oqam systems like other orthogonal frequency division multiplexing ofdm systems ofdm systems based on offset quadrature amplitude modulation ofdm oqam are very sensitive to carrier frequency offset in this paper a new blind carrier frequency offset estimator is developed for ofdm oqam systems by exploiting the noncircularity of the received ofdm oqam signal since the received signal exhibits conjugate cyclic frequencies at twice the carrier frequency offset the frequency estimator is designed by maximizing a cost function expressed in terms of the sample conjugate cyclocorrelations the theoretical asymptotic large sample performance analysis of the proposed estimator is established computer simulations are presented to illustrate the performance of the estimator it is shown that the proposed estimator is very accurate whenever it is well initialized therefore the proposed estimator appears to be very well adapted for a tracking mode rather than for an acquisition mode

synthesizing low autocorrelation and low papr ofdm sequences under spectral constraints through convex optimization and gs algorithm sequences with low autocorrelation ac and low peak to average power ratio papr are desired in many communication or signal processing applications this work investigates the synthesis of ofdm sequences with the desired low ac and low papr under spectral constraints the spectral constraints limit the maximum allowable power on each subcarrier to avoid interference on particular reserved bands and undesirable dc offset the first part of this work discusses the design of sequences with periodic ac property under spectral constraints specifically we present a convex optimization method for synthesizing ofdm sequences with minimized peak sidelobe level psl or weighted sum of sidelobe levels wssl of the periodic ac function within specified time lags the design objective to be minimized can also be a certain convex function of the sequence ac sidelobes furthermore we present methods based on gerchberg saxton gs algorithm to decrease the papr of the sequences while maintaining the optimized ac characteristic the second part of this work investigates the aperiodic ac under spectral constraints in this case the optimal sequence design problem is nonconvex by relaxing the nonconvex problem to a convex problem we provide lower bounds for psl and wssl of the aperiodic ac function based on the optimal solution for the relaxed convex problem we present an efficient algorithm to find sequences with low papr and near optimal aperiodic ac property while the spectral constraints are satisfied

spaces and maps approximation and fixed points abstract a general approximation property for topological spaces is studied in relation with fixed point theory for set valued maps a particular instance of this property is the admissibility in the sense of klee examples of convex sets of topological spaces equipped with a local topological convexity structure as well as general classes of approximative neighborhood retracts are shown to have this approximation property a general topological principle on the preservation of the fixed point property under this space approximation is proved it allows the passage from basic classes of spaces to more elaborate ones for general classes of nonconvex set valued maps

fixed point theorems for better admissible multimaps on almost convex sets abstract we obtain new fixed point theorems on multimaps in the class b p defined on almost convex subsets of topological vector spaces our main results are applied to deduce various fixed point theorems coincidence theorems almost fixed point theorems intersection theorems and minimax theorems consequently our new results generalize well known works of kakutani fan browder himmelberg lassonde and others

on maximum likelihood blind synchronization over wssus channels for ofdm systems various blind synchronization methods built on the maximum likelihood ml principle have been proposed where the addressed scenarios include additive white gaussian noise awgn single path fading and multipath fading channels we consider ml blind synchronization over wide sense stationary uncorrelated scattering wssus channels different from existing studies we exploit a more complete signal correlation function and find the carrier frequency offset estimate to be the solution of a quartic equation rather than the phase angle of a complex number as the truly ml synchronizer dubbed mle is very complicated we also derive a reduced complexity alternative dubbed rce it is found that the rce yields indistinguishable performance from the mle at a somewhat lower complexity than an existing rival we also present an in depth theoretical analysis and comparison of the performance of various methods simulations show that the proposed methods yield rather robust performance in modeling errors of the fading rate and the channel power delay profile pdp

ml based symbol timing and frequency offset estimation for ofdm systems with noncircular transmissions this paper deals with the problem of joint symbol timing and carrier frequency offset cfo estimation in orthogonal frequency division multiplexing ofdm systems with noncircular nc transmissions maximum likelihood ml estimators of symbol timing and cfo have been derived under the assumption of nondispersive channel and by modeling the ofdm signal vector as a circular complex gaussian random vector c cgrv the gaussian assumption is reasonable when the number of subcarriers is sufficiently large however if the data symbols belong to an nc constellation the received signal vector becomes an nc cgrv i e a cgrv whose relation matrix defined as the statistical expectation of the product between the vector and its transpose is not identically zero hence in this case previously mentioned estimators termed mlc estimators are not ml estimators in this paper by exploiting the joint probability density function for nc cgrvs ml estimators are derived moreover since their implementation complexity is high feasible computational algorithms are considered finally refined symbol timing estimators apt to counteract the degrading effects of intersymbol interference isi in dispersive channels are suggested the performance of the derived estimators is assessed via computer simulation and compared with that of mlc estimators and that of modified mlc mmlc estimators exploiting only isi free samples of the cyclic prefix

fixed point theorems for the ψ set contraction mapping on almost convex sets abstract in this paper we first discuss the properties of the almost convex subsets of a hausdorff topological vector space then in the setting of the almost convex sets we establish some fixed point theorems for the two k k m and b d type set valued mappings with either set contraction or 1 set contraction next we also establish new cycle point theorems for three set valued mappings our results generalize the results of chang et al t h chang c l yen kkm property and fixed point theorems j math anal appl 203 1996 224 235 and park s park fixed point theorems for better admissible multimaps on almost convex sets j math anal appl 329 2007 690 702

blind estimation of ofdm carrier frequency offset via oversampling blind deterministic estimation of the orthogonal frequency division multiplexing ofdm frequency offset via oversampling is proposed in this paper this method utilizes the intrinsic phase shift of neighboring sample points incurred by the frequency offset that is common among all subcarriers the proposed method is data efficient it requires only a single ofdm symbol to achieve reliable estimation hence making it more suitable to systems with stringent delay requirement and mobility induced channel variation the proposed scheme is devised to perfectly retrieve frequency offset in the absence of noise quite remarkably we show that in the presence of channel noise this intuitive scheme is indeed the maximum likelihood estimate of the carrier frequency offset the possible presence of virtual carriers are also accommodated in the system model and some interesting observations are obtained the cramer rao lower bound is derived for the oversampling based signal model and we show through numerical simulation that the proposed algorithm is efficient practical issues such as identifiability the front end filter bandwidth and the possible presence of correlated noises are also carefully addressed

fast adaptive equalization diversity combining for time varying dispersive channels we examine adaptive equalization and diversity combining methods for fast rayleigh fading frequency selective channels we assume a block adaptive receiver in which the receiver coefficients are obtained from feedforward channel estimation for the feedforward channel estimation we propose a novel reduced dimension channel estimation procedure where the number of unknown parameters are reduced using a priori information of the transmit shaping filter s impulse response fewer unknown parameters require a shorter training sequence we obtain least squares maximum likelihood and maximum a posteriori map estimators for the reduced dimension channel estimation problem for symbol detection we propose the use of a matched filtered diversity combining decision feedback equalizer dfe instead of a straightforward diversity combining dfe the matched filter form has lower computational complexity and provides a well conditioned matrix inversion to cope with fast time varying channels we introduce a new dfe coefficient computation algorithm which is obtained by incorporating the channel variation during the decision delay into the minimum mean square error mmse criterion we refer to this as the non toeplitz dfe nt dfe we also show the feasibility of a suboptimal receiver which has a lower complexity than a recursive least squares adaptation with performance close to the optimal nt dfe

a combined timing and frequency synchronization and channel estimation for ofdm this letter addresses training signal based combined timing and frequency synchronization and channel estimation for orthogonal frequency division multiplexing systems the proposed scheme consists of two stages at the first stage coarse timing and frequency offset estimates are obtained based on these estimates a coarse channel response estimate is obtained the timing and frequency offset estimates at the second stage are obtained by maximum likelihood ml realization based on a sliding observation vector then ml channel estimation is performed a means of complexity reduction by an adaptive scheme is also presented the simulation results show that the proposed combined approach performs quite well and circumvents the problem of mismatch among individual synchronization tasks