symbol level adaptive modulation for coded ofdm on block fading channels it has recently been recognized by many researchers that adaptive modulation is most effective when the channel diversity order is small in this letter we propose a simple adaptive modulation scheme for orthogonal frequency division multiplexing ofdm systems on channels that provide a small order of diversity the proposed adaptation algorithm is based on a novel and very simple analytical formula we derive for the performance of bicm on block fading channels simulation results show that the derived analytical formula is very tight when the targeted bit error probability is small ofdm systems on indoor channels provide small orders of diversity and form an ideal scenario for adaptation in order to keep system complexity and feedback requirements at a minimum we will consider symbol level adaptive modulation wherein all the subcarriers in an ofdm symbol use the same modulation

perturbation of the equilibrium for a totally asymmetric stick process in one dimension we study the evolution of a small perturbation of the equilibrium of a totally asymmetric one dimensional interacting system the model we take as an example is hammersley s process as seen from a tagged particle which can be viewed as a process of interacting positive valued stick heights on the sites of z it is known that under euler scaling space and time scale n the empirical stick profile obeys the burgers equation we refine this result in two ways if the process starts close enough to equilibrium then over times n for 1 v 3 and up to errors that vanish in hydrodynamic scale the dynamics merely translates the initial stick configuration in particular on the hydrodynamic time scale diffusive fluctuations are translated rigidly a time evolution for the perturbation is visible under a particular family of scalings over times n 1 v 3 2 a perturbation of order n 1 from equilibrium follows the inviscid burgers equation the results for the stick model are derived from asymptotic results for tagged particles in hammersley s process

optimal throughput diversity delay tradeoff in mimo arq block fading channels in this paper we consider an automatic repeat request arq retransmission protocol signaling over a block fading multiple input multiple output mimo channel unlike previous work we allow for multiple fading blocks within each transmission arq round and we constrain the transmitter to fixed rate codes constructed over complex signal constellations in particular we examine the general case of average input power constrained con stellations with a fixed signaling alphabet of finite cardinality this scenario is a suitable model for practical wireless communications systems employing orthogonal frequency division multiplexing ofdm techniques over a mimo arq channel two cases of fading dynamics are considered namely short term static fading where channel fading gains change randomly for each arq round and long term static fading where channel fading gains remain constant over all arq rounds pertaining to a given message as our main result we prove that for the block fading mimo arq channel with a fixed signaling alphabet satisfying a short term power constraint the optimal signal to noise ratio snr exponent is given by a modified singleton bound relating all the system parameters to demonstrate the practical significance of the theoretical analysis we present numerical results showing that practical singleton bound achieving maximum distance separable codes achieve the optimal snr exponent

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

on improved bounds on the decoding error probability of block codes over interleaved fading channels with applications to turbo like codes we derive here improved upper bounds on the decoding error probability of block codes which are transmitted over fully interleaved rician fading channels coherently detected and maximum likelihood ml decoded we assume that the fading coefficients during each symbol are statistically independent due to a perfect channel interleaver and that perfect estimates of these fading coefficients are provided to the receiver the improved upper bounds on the block and bit error probabilities are derived for fully interleaved fading channels with various orders of space diversity and are found by generalizing some previously introduced upper bounds for the binary input additive white gaussian nose awgn channel the advantage of these bounds over the ubiquitous union bound is demonstrated for some ensembles of turbo codes and low density parity check ldpc codes and it is especially pronounced in a portion of the rate region exceeding the cutoff rate our generalization of the duman and salehi bound duman and salehi 1998 duman 1998 which is based on certain variations of gallager s 1965 bounding technique is demonstrated to be the tightest reported upper bound we therefore apply it to calculate numerically upper bounds on the thresholds of some ensembles of turbo like codes referring to the optimal ml decoding for certain ensembles of uniformly interleaved turbo codes the upper bounds derived here also indicate good match with computer simulation results of efficient iterative decoding algorithms

optimal power control for ldpc codes in block fading channels we study the error probability of ldpc codes in delay limited block fading channels with channel state information csi at the transmitter and the receiver we derive the optimal power allocation algorithms for ldpc codes with specific degree distributions using multi edge type density evolution error boundaries the resulting performance approaches the outage probability for a number of power constraints furthermore we adapt the algorithm for finite length codes and show that the proposed algorithm enables gains larger than 10 db over uniform power allocation the method is valid for general possibly correlated fading distributions this represents the first analysis of specific ldpc codes over block fading channels with full csi

low density graph codes for coded cooperation on slow fading relay channels we study low density parity check ldpc codes with iterative decoding on block fading bf relay channels we consider two users that employ coded cooperation a variant of decode and forward with a smaller outage probability than the latter an outage probability analysis for discrete constellations shows that full diversity can be achieved only when the coding rate does not exceed a maximum value that depends on the level of cooperation we derive a new code structure by extending the previously published full diversity root ldpc code designed for the bf point to point channel to exhibit a rate compatibility property which is necessary for coded cooperation we estimate the asymptotic performance through a new density evolution analysis and the word error rate performance is determined for finite length codes we show that our code construction exhibits near outage limit performance for all block lengths and for a range of coding rates up to 0 5 which is the highest possible coding rate for two cooperating users

microscopic shape of shocks in a domain growth model considering the hydrodynamical limit of some interacting particle systems leads to hyperbolic differential equation for the conserved quantities e g the inviscid burgers equation for the simple exclusion process the physical solutions of these partial differential equations develop discontinuities called shocks the microscopic structure of these shocks is of much interest and far from being well understood we introduce a domain growth model in which we find a stationary in time product measure for the model as seen from a defect tracer or second class particle traveling with the shock we also show that under some natural assumptions valid for a wider class of domain growth models no other model has stationary product measure as seen from the moving defect tracer

coded modulation in the block fading channel coding theorems and code construction we consider coded modulation schemes for the block fading channel in the setting where a codeword spans a finite number n of fading degrees of freedom we show that coded modulations of rate r bit per complex dimension over a finite signal set spl chi spl sube spl copf of size 2 sup m achieve the optimal rate diversity tradeoff given by the singleton bound spl delta n m r 1 spl lfloor n 1 r m spl rfloor for r spl isin 0 m spl rfloor furthermore we show also that the popular bit interleaved coded modulation achieves the same optimal rate diversity tradeoff we present a novel coded modulation construction based on blockwise concatenation that systematically yields singleton bound achieving turbo like codes defined over an arbitrary signal set spl chi spl sub spl copf the proposed blockwise concatenation significantly outperforms conventional serial and parallel turbo codes in the block fading channel we analyze the ensemble average performance under maximum likelihood ml decoding of the proposed codes by means of upper bounds and tight approximations we show that differently from the additive white gaussian noise awgn and fully interleaved fading cases belief propagation iterative decoding performs very close to ml on the block fading channel for any signal to noise ratio snr and even for relatively short block lengths we also show that at constant decoding complexity per information bit the proposed codes perform close to the information outage probability for any block length while standard block codes e g obtained by trellis termination of convolutional codes have a gap from outage that increases with the block length this is a different and more subtle manifestation of the so called interleaving gain of turbo codes

coded modulation with mismatched csit over mimo block fading channels reliable communication over delay constrained multiple input multiple output mimo block fading channels with discrete inputs and mismatched imperfect channel state information at the transmitter csit is studied the csit mismatch is modeled as gaussian random variables whose variances decay as a power of the signal to noise ratio snr a special focus is placed on the large snr decay of the error and outage probabilities when power control with long term power constraints is used without explicitly characterizing the corresponding power allocation algorithms we derive the outage exponent as a function of the system parameters including the csit noise variance exponent and the exponent of the peak power constraint it is shown that csit even if noisy is always beneficial and leads to important gains in terms of exponents

on the asymptotic input output weight distributions and thresholds of convolutional and turbo like encoders we present a general method for computing the asymptotic input output weight distribution of convolutional encoders in some instances one can derive explicit analytic expressions in general though to determine the growth rate of the input output weight distribution for a particular normalized input weight spl kappa and output weight spl omega a system of polynomial equations has to be solved this method is then used to determine the asymptotic weight distribution of various concatenated code ensembles and to derive lower bounds on the thresholds of these ensembles under maximum likelihood ml decoding

multiple shocks in bricklayers model in bricklayers model which is a generalization of the misanthrope processes we show that a nontrivial class of product distributions is closed under the time evolution of the process this class also includes measures fitting to shock data of the limiting pde in particular we show that shocks of this type with discontinuity of size one perform ordinary nearest neighbor random walks only interacting in an attractive way via their jump rates our results are related to those of belitsky and schutz 4 on the simple exclusion process although we do not use quantum formalism as they do the structures we find are described from a fixed position similar ones were found in balazs 2 valak as seen from the random position of the second class particle

improved upper bounds on the ml decoding error probability of parallel and serial concatenated turbo codes via their ensemble distance spectrum the ensemble performance of parallel and serial concatenated turbo codes is considered where the ensemble is generated by a uniform choice of the interleaver and of the component codes taken from the set of time varying recursive systematic convolutional codes following the derivation of the input output weight enumeration functions of the ensembles of random parallel and serial concatenated turbo codes the tangential sphere upper bound is employed to provide improved upper bounds on the block and bit error probabilities of these ensembles of codes for the binary input additive white gaussian noise awgn channel based on coherent detection of equi energy antipodal signals and maximum likelihood decoding the influence of the interleaver length and the memory length of the component codes is investigated the improved bounding technique proposed here is compared to the conventional union bound and to a alternative bounding technique by duman and salehi 1998 which incorporates modified gallager bounds the advantage of the derived bounds is demonstrated for a variety of parallel and serial concatenated coding schemes with either fixed or random recursive systematic convolutional component codes and it is especially pronounced in the region exceeding the cutoff rate where the performance of turbo codes is most appealing these upper bounds are also compared to simulation results of the iterative decoding algorithm

spectral gap for zero range dynamics we give a lower bound on the spectral gap for symmetric zero range processes under some conditions on the rate function we show that the gap shrinks as n 2 independent of the density for the dynamics localized on a cube of size n d we follow the method outlined by lu and yau where a similar spectral gap is proved for kawasaki dynamics

spectral gap and logarithmic sobolev inequality for kawasaki and glauber dynamics we prove that the spectral gap of the kawasaki dynamics shrink at the rate of 1 l2 for cubes of sizel provided that some mixing conditions are satisfied we also prove that the logarithmic sobolev inequality for the glauber dynamics in standard cubes holds uniformly in the size of the cube if the dobrushin shlosman mixing condition holds for standard cubes

how to initialize a second class particle we identify the ballistically and diffusively rescaled limit distribution of the second class particle position in a wide range of asymmetric and symmetric interacting particle systems with established hydrodynamic behavior respectively including zero range misanthrope and many other models the initial condition is a step profile which in some classical cases of asymmetric models gives rise to a rarefaction fan scenario we also point out a model with nonconcave nonconvex hydrodynamics where the rescaled second class particle distribution has both continuous and discrete counterparts the results follow from a substantial generalization of ferrari and kipnis arguments ann inst h poincare 31 1995 143 154 for the totally asymmetric simple exclusion process the main novelty is the introduction of a signed coupling measure as initial data which nevertheless results in a proper probability initial distribution for the site of the second class particle and makes the extension possible we also reveal in full generality a very interesting invariance property of the one site marginal distribution of the process underneath the second class particle which in particular proves the intrinsicality of our choice for the initial distribution finally we give a lower estimate on the probability of survival of a second class particle antiparticle pair

upper bounds to error probabilities of coded systems beyond the cutoff rate a family of upper bounds to error probabilities of coded systems was recently proposed by d divsalar see ieee communication theory workshop 1999 jpl tmo prog rep 42 139 1999 these bounds are valid for transmission over the additive white gaussian noise channel and require only the knowledge of the weight spectrum of the code words after illustrating these bounds we extend them to fading channels contrary to the union bound our bounds maintain their effectiveness below the signal to noise ratio snr at which the cutoff rate of the channel equals the rate of the code some applications are shown first we derive upper bounds to the minimum snr necessary to achieve zero error probability as the code block length increases to infinity next we use our bounds to predict the performance of turbo codes and low density parity check codes

coding for parallel channels gallager bounds and applications to turbo like codes the transmission of coded communication systems is widely modeled to take place over a set of parallel channels this model is used for transmission over block fading channels rate compatible puncturing of turbo like codes multicarrier signaling multilevel coding etc new upper bounds on the maximum likelihood ml decoding error probability are derived in the parallel channel setting we focus on the generalization of the gallager type bounds and discuss the connections between some versions of these bounds the tightness of these bounds for parallel channels is exemplified for structured ensembles of turbo codes repeat accumulate ra codes and some of their recent variations e g punctured accumulate repeat accumulate codes the bounds on the decoding error probability of an ml decoder are compared to computer simulations of iterative decoding the new bounds show a remarkable improvement over the union bound and some other previously reported bounds for independent parallel channels this improvement is exemplified for relatively short block lengths and it is pronounced when the block length is increased in the asymptotic case where we let the block length tend to infinity inner bounds on the attainable channel regions of modern coding techniques under ml decoding are obtained based solely on the asymptotic growth rates of the average distance spectra of these code ensembles

perturbation of singular equilibria of hyperbolic two component systems a universal hydrodynamic limit we consider one dimensional locally finite interacting particle systems with two conservation laws which under the eulerian hydrodynamic limit lead to two by two systems of conservation laws t x u 0 t u x u 0

onsager relations and eulerian hydrodynamic limit for systems with several conservation laws we present the derivation of the hydrodynamic limit under eulerian scaling for a general class of one dimensional interacting particle systems with two or more conservation laws following yau s relative entropy method it turns out that in case of more than one conservation laws in order that the system exhibit hydrodynamic behaviour some particular identities reminiscent of onsager s reciprocity relations must hold we check validity of these identities whenever a stationary measure with product structure exists it also follows that as a general rule the equilibrium thermodynamic entropy as function of the densities of the conserved variables is a globally convex lax entropy of the hyperbolic systems of conservation laws arising as hydrodynamic limit as concrete examples we also present a number of models modeling deposition or domain growth phenomena the onsager relations arising in the context of hydrodynamic limits under hyperbolic scaling seem to be novel the fact that equilibrium thermodynamic entropy is lax entropy for the arising euler equations was noticed earlier in the context of hamiltonian systems with weak noise see ref 7

on the performance analysis of space time codes in quasi static rayleigh fading channels in this paper we analyze the performance of space time codes by deriving a new approximation of the frame error probabilities for space time trellis coded modulations over quasi static rayleigh fading channels we take advantage of two techniques the modified bounding technique and the limiting before averaging technique to tighten the upper bound in addition we establish a theorem that enables us to reduce the computation and memory needed to calculate the frame error rate fer approximation the newly derived approximation is very tight requires only the distance spectrum of the space time code and can be computed through single numerical integration numerical results exhibit that the new approximation is much closer to the simulation results than other existing bounds are especially in the case of one receive antenna

coding and decoding for the dynamic decode and forward relay protocol we study the dynamic decode and forward ddf protocol for a single half duplex relay single antenna channel with quasi static fading the ddf protocol is well known and has been analyzed in terms of the diversity multiplexing tradeoff dmt in the infinite block length limit we characterize the finite block length dmt and give new explicit code constructions the finite block length analysis illuminates a few key aspects that have been neglected in the previous literature 1 we show that one dominating cause of degradation with respect to the infinite block length regime is the event of decoding error at the relay 2 we explicitly take into account the fact that the destination does not generally know a priori the relay decision time at which the relay switches from listening to transmit mode both of the above problems can be tackled by a careful design of the decoding algorithm in particular we introduce a decision rejection criterion at the relay based on forney s decision rule a variant of the neyman pearson rule such that the relay triggers transmission only when its decision is reliable also we show that a receiver based on the generalized likelihood ratio test glrt rule that jointly decodes the relay decision time and the information message achieves the optimal dmt our results show that no cyclic redundancy check crc for error detection or additional protocol overhead to communicate the decision time are needed for ddf finally we investigate the use of minimum mean squared error generalized decision feedback equalizer mmse gdfe lattice decoding at both the relay and the destination and show that it provides near optimal performance at moderate complexity

new gallager bounds in block fading channels in this paper we propose a new upper bound on the error performance of binary linear codes over block fading channels by employing gallager s first and second bounding techniques as the proposed bound is numerically intensive in its general form we consider two special cases namely the spherical bound and the ds2 exponential bound which are found to be tight in nonergodic and near ergodic block fading channels respectively the tightness of the proposed bounds is demonstrated for turbo codes many existing bounds for quasistatic or fully interleaved fading channels can be viewed as special cases of the proposed gallager bound

tight exponential upper bounds on the ml decoding error probability of block codes over fully interleaved fading channels we derive tight exponential upper bounds on the decoding error probability of block codes which are operating over fully interleaved rician fading channels coherently detected and maximum likelihood decoded it is assumed that the fading samples are statistically independent and that perfect estimates of these samples are provided to the decoder these upper bounds on the bit and block error probabilities are based on certain variations of the gallager bounds these bounds do not require integration in their final version and they are reasonably tight in a certain portion of the rate region exceeding the cutoff rate of the channel by inserting interconnections between these bounds we show that they are generalized versions of some reported bounds for the binary input additive white gaussian noise channel

a general formula for channel capacity a formula for the capacity of arbitrary single user channels without feedback not necessarily information stable stationary etc is proved capacity is shown to equal the supremum over all input processes of the input output inf information rate defined as the liminf in probability of the normalized information density the key to this result is a new converse approach based on a simple new lower bound on the error probability of m ary hypothesis tests among equiprobable hypotheses a necessary and sufficient condition for the validity of the strong converse is given as well as general expressions for spl epsiv capacity

coding in the block erasure channel in this correspondence we study an m ary block erasure channel with b blocks where with probability epsi a block of l coded symbols is erased the behavior of the error probability of coded systems over such channels is studied and we show that if the code is diversity wise maximum distance separable its word error probability is equal to the outage probability which admits a very simple expression this correspondence is intended to complement the error probability analysis in previous work by lapidoth and shed some light on the design of coding schemes for nonergodic channels

multifrequency trellis coding with low delay for fading channels an l frequency trellis coding scheme designed for fading channels that provides diversity up to order l is described l frequency coding is advantageous over channel coding schemes that achieve implicit time diversity through trellis coding in conjunction with time interleaving because it requires negligible end to end delay the authors derive an upper bound for the probability of symbol error of the l frequency code based on this upper bound they then deduce the design criteria for optimum l frequency codes a numerical approximation to this upper bound and the design of a two state and two four state two frequency codes are presented through simulations it was found that relative to the traditional dual frequency diversity approach the two state and four state codes achieve 3 and 4 db coding gains respectively this energy efficiency gain can be translated into a spectral efficiency gain a brief discussion on the difference in code design techniques for the gaussian channel and the fading channel is also presented

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

between equilibrium fluctuations and eulerian scaling perturbation of equilibrium for a class of deposition models we investigate propagation of perturbations of equilibrium states for a wide class of 1d interacting particle systems the class of systems considered incorporates zero range k exclusion misanthropic bricklayers models and much more we do not assume attractivity of the interactions we apply yau s relative entropy method rather than coupling arguments the result is partial extension of t seppalainen s recent paper for 0 1 5 fixed we prove that rescaling microscopic space and time by n respectively n1 the macroscopic evolution of perturbations of microscopic order n of the equilibrium states is governed by burgers equation the same statement should hold for 0 1 2 as in seppalainen s cited paper but our method does not seem to work for 1 5

processus des misanthropes we consider a system of identical interacting particles moving on the lattice d the rate at which a particle at the site x jumps to the site y is p y x b x y where p is an irreducible probability on d and b x y is an increasing resp decreasing function of the number x resp y of particles at site x resp y we study the convergence of the system to equilibrium and describe the invariant measures

a tight lower bound to the outage probability of discrete input block fading channels in this correspondence a tight lower bound to the outage probability of discrete input nakagami m block fading channels is proposed the approach permits an efficient method for numerical evaluation of the bound providing an additional tool for system design the optimal rate diversity tradeoff for the nakagami m block fading channel is also derived and a tight upper bound is obtained for the optimal coding gain constant

controllability and adaptation of linear time invariant systems under irregular and markovian sampling this paper investigates controllability for linear time invariant systems under irregular and random sampling and develops adaptive control algorithms with respect to sampling intervals using block erasure channels as the main motivating communication platform it first establishes a sufficient condition on sampling density that ensures controllability of sampled systems which is necessary for feedback design and adaptation then it continues with causal adaptive feedback algorithms to accommodate time varying sampling intervals implementation of such algorithms encounters technical challenges because future sampling intervals are uncertain or random under deterministic slowly varying and stochastic infrequent markovian jumping sampling intervals overall system stability is established simulation results are used to illustrate the algorithms and their effectiveness

pragmatic space time trellis codes gtf based design for block fading channels the pragmatic approach for the construction of space time codes over block fading channels leads to low complexity encoders decoders making them suitable for various applications including cooperative communications we propose a design methodology for pragmatic space time codes which is based on an extension of the concept of generalized transfer function our search algorithm provides code generators for arbitrary number of states antennas and fading rates numerical results show that the performance of the pragmatic space time codes obtained by our design methodology is generally better than that of previously known space time trellis codes in block fading channels

coded diversity on block fading channels this paper considers coded diversity schemes over block fading rician channels using random coding techniques two random coding upper bounds on the error probability of block codes are derived a new bound and a simpler but looser bound assuming binary input distribution also a new lower bound for any block code is derived using the strong converse to channel coding theorem the lower bound shows that the new random coding upper bound is quite tight furthermore it is shown that the maximum achievable diversity order in a block fading channel with finite interleaving depends not only on the number of subchannels l but also on the code rate r and that the performance can only marginally be improved by increasing the block length of the code the random coding upper bound and the lower bound are shown to converge to the capacity outage for large channel block lengths n demonstrating that the capacity outage can be used for estimating the error probability of coded diversity schemes

a new class of iterative equalizers for space time bicm over mimo block fading multipath awgn channel this paper addresses the issue of advanced equalization methods for space time communications over multiple input multiple output block fading channel with intersymbol interference instead of resorting to conventional multiuser detection techniques based on the straightforward analogy between antennas and users we adopt a different point of view and separate time equalization from space equalization thus introducing a higher degree of freedom in the overall space time equalizer design time domain equalization relies on minimum mean square error criterion and operates on multidimensional modulation symbols whose individual components can be detected in accordance with another criterion in particular when the optimum maximum a posteriori criterion is chosen substantial performance gains over conventional space time turbo equalization have been observed for different transmission scenarios at the price of an increased albeit manageable computational complexity

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

further results on convolutional code search for block fading channels this correspondence presents results of code search for convolutional codes over block fading channels bfcs search criteria are based on a union bound approach which exploits the concept of generalized transfer function gtf of the error trellis diagram a new asymptotic bound is derived and the performance of the codes found using our search criterion is compared analytically and by numerical simulation with already existing codes