waashk/dblp huggingface dataset:
diversity-multiplexing tradeoff in isi channels. the optimal diversity-multiplexing tradeoff curve for the intersymbol interference (isi) channel is computed and various equalizers are analyzed using this performance metric. maximum-likelihood signal decoding (mlsd) and decision feedback equalization (dfe) equalizers achieve the optimal tradeoff without coding, but zero forcing (zf) and minimum mean-square-error (mmse) equalizers do not. however if each transmission block is ended with a period of silence lasting the coherence time of the channel, both zf and mmse equalizers become diversity-multiplexing optimal. this suggests that the bulk of the performance gain obtained by replacing linear decoders with computationally intensive ones such as orthogonal frequency-division multiplexing (ofdm) or viterbi, can be realized in much simpler fashion-with a small modification to the transmit scheme.
optimization of information rate upper and lower bounds for channels with memory. we consider the problem of minimizing upper bounds and maximizing lower bounds on information rates of stationary and ergodic discrete-time channels with memory. the channels we consider can have a finite number of states, such as partial response channels, or they can have an infinite state space, such as time-varying fading channels. we optimize recently proposed information rate bounds for such channels, which make use of auxiliary finite-state machine channels (fsmcs). our main contribution in this paper is to provide iterative expectation-maximization (em) type algorithms to optimize the parameters of the auxiliary fsmc to tighten these bounds. we provide an explicit, iterative algorithm that improves the upper bound at each iteration. we also provide an effective method for iteratively optimizing the lower bound. to demonstrate the effectiveness of our algorithms, we provide several examples of partial response and fading channels where the proposed optimization techniques significantly tighten the initial upper and lower bounds. finally, we compare our results with results obtained by the conjugate gradient optimization algorithm and an improved variation of the simplex algorithm, called soblex. while the computational complexities of our algorithms are similar to the conjugate gradient method and less than the soblex algorithm, our algorithms robustly find the tightest bounds. interestingly, from a channel coding/decoding perspective, optimizing the lower bound is related to increasing the achievable mismatched information rate, i.e., the information rate of a communication system where the decoder at the receiver is matched to the auxiliary channel, and not to the original channel.
capacity of steganographic channels. this work investigates a central problem in steganography, that is: how much data can safely be hidden without being detected? to answer this question, a formal definition of steganographic capacity is presented. once this has been defined, a general formula for the capacity is developed. the formula is applicable to a very broad spectrum of channels due to the use of an information-spectrum approach. this approach allows for the analysis of arbitrary steganalyzers as well as nonstationary, nonergodic encoder and attack channels. after the general formula is presented, various simplifications are applied to gain insight into example hiding and detection methodologies. finally, the context and applications of the work are summarized in a general discussion.
optimal frequency hopping sequences: auto- and cross-correlation properties. frequency hopping (fh) sequences play a key role in frequency hopping spread spectrum communication systems. in order to evaluate the performance of fh sequences, lempel and greenberger (1974) and peng and fan (2004) derived lower bounds on their hamming auto- and cross-correlations. in this paper, we construct families of fh sequences with hamming correlations meeting those bounds by combinatorial and algebraic techniques. we first construct optimal families consisting of a single fh sequence with maximum hamming correlation equal to 2 from a combinatorial approach. then we investigate families consisting of multiple fh sequences. we provide a combinatorial characterization for such families, and present a recursive method to construct them by means of this characterization. we also describe two algebraic constructions for such families of fh sequences, generalizing those of ding, moisio, and yuan (2007). as a consequence, many new optimal families of fh sequences are obtained.
parity forwarding for multiple-relay networks. this paper proposes a relaying strategy for the multiple-relay network in which each relay decodes a selection of transmitted messages by other transmitting terminals, and forwards parities of the decoded codewords. this protocol improves the previously known achievable rate of the decode-and-forward (df) strategy for multirelay networks by allowing relays to decode only a selection of messages from relays with strong links to it. hence, each relay may have several choices as to which messages to decode, and for a given network many different parity forwarding protocols may exist. a tree structure is devised to characterize a class of parity forwarding protocols for an arbitrary multirelay network. based on this tree structure, closed-form expressions for the achievable rates of these df schemes are derived. it is shown that parity forwarding is capacity achieving for new forms of degraded relay networks.
reliable communication in the absence of a common clock. we introduce the continuous time asynchronous channel as a model for time jitter in a communication system with no common clock between the transmitter and the receiver. we have obtained a simple characterization for an optimal zero-error self-synchronizable code for the asynchronous channel. the capacity of this channel is determined by both a combinatorial approach and a probabilistic approach. our results unveil the somewhat surprising fact that it is not necessary for the receiver clock to resynchronize with the transmitter clock within a fixed maximum time in order to achieve reliable communication. this means that no upper limit should be imposed on the run lengths of the self-synchronization code as in the case of run-length limited (rll) codes which are commonly used in magnetic recording.
a family of m -sequences with five-valued cross correlation. finding the cross correlation between two m-sequences {st} and {sdt} of the same period 2m - 1, that differ by a decimation d, has been a popular research problem since the 1960s. many cases with three- and four-valued correlation have been determined. several values of d are known to lead to five-valued cross correlation but their exact correlation distribution has been open. the correlation distribution is completely determined for one of these families with five-valued cross correlation by using evaluations of certain exponential sums including kloosterman sums. the decimation considered is the special decimation d = 22k+1/2k+1 where m is odd and k = 1, i.e., d = 5/3. the paper introduces some techniques that may be useful to obtain further results on related decimations.
the minimum distance of turbo-like codes. worst-case upper bounds are derived on the minimum distance of parallel concatenated turbo codes, serially concatenated convolutional codes, repeat-accumulate codes, repeat-convolute codes, and generalizations of these codes obtained by allowing nonlinear and large-memory constituent codes. it is shown that parallel-concatenated turbo codes and repeat-convolute codes with sub-linear memory are asymptotically bad. it is also shown that depth-two serially concatenated codes with constant-memory outer codes and sublinear-memory inner codes are asymptotically bad. most of these upper bounds hold even when the convolutional encoders are replaced by general finite-state automata encoders. in contrast, it is proven that depth-three serially concatenated codes obtained by concatenating a repetition code with two accumulator codes through random permutations can be asymptotically good.
recursive constructions of detecting matrices for multiuser coding: a unifying approach. detecting matrices are a class of combinatorial objects originated from the coin weighing problem of söderberg and shapiro in the early 1960s. in this paper, various known recursive construction techniques for binary, bipolar, and ternary detecting matrices are reexamined in a unifying framework. new, general recursive constructions of detecting matrices, which include previous recursive constructions as special cases, are derived. such matrices find applications in multiuser coding since they are equivalent to a certain class of uniquely decodable multiuser codes for the binary adder channel. interestingly, it is found that among the three kinds of detecting matrices, ternary detecting matrices are of fundamental significance from the combinatorial theoretic, as well as from the multiuser coding application, point of view.
a new outer bound and the noisy-interference sum-rate capacity for gaussian interference channels. a new outer bound on the capacity region of gaussian interference channels is developed. the bound combines and improves existing genie-aided methods and is shown to give the sum-rate capacity for noisy interference as defined in this paper. specifically, it is shown that if the channel crosstalk coefficient magnitudes lie below thresholds defined by the power constraints then single-user detection at each receiver is sum-rate optimal, i. treating the interference as noise incurs no loss in performance. this is the first capacity result for the gaussian interference channel with weak to moderate interference. furthermore, for certain mixed (weak and strong) interference scenarios, the new outer bounds give a corner point of the capacity region.
the capacity region of a class of semideterministic interference channels. the capacity region of a class of discrete memoryless interference channels with common information is established. the setup is similar to the class of deterministic interference channels without common information studied by el gamal and costa, which was later extended to the class of deterministic interference channels with common information. in this paper, certain conditions that were originally imposed by el gamal and costa are relaxed and it is shown, by a specific example, that this new class of interference channels is strictly larger than the class of deterministic interference channels previously studied. in fact, the result of this paper is obtained by combining the class of deterministic interference channels with the class of discrete memoryless interference channels with strong interference. hence, it also includes the capacity region of the class of discrete memoryless interference channels with strong interference as a special case.
high-snr analysis of outage-limited communications with bursty and delay-limited information. this work analyzes the high-snr asymptotic error performance of outage-limited communications with fading, where the number of bits that arrive at the transmitter during any timeslot is random but the delivery of bits at the receiver must adhere to a strict delay limitation. specifically, bit errors are caused by erroneous decoding at the receiver or violation the strict delay constraint. under certain scaling of the statistics of the bit-arrival process with snr, this paper shows that the optimal decay behavior of the asymptotic total probability of bit error depends on how fast the burstiness of the source scales down with snr. if the source burstiness scales down too slowly, the total probability of error is asymptotically dominated by delay-violation events. on the other hand, if the source burstiness scales down too quickly, the total probability of error is asymptotically dominated by channel-error events. however, at the proper scaling, where the burstiness scales linearly with 1/√log snr and at the optimal coding duration and transmission rate, the occurrences of channel errors and delay-violation errors are asymptotically balanced. in this latter case, the optimal exponent of the total probability of error reveals a tradeoff that addresses the question of how much of the allowable time and rate should be used for gaining reliability over the channel and how much for accommodating the burstiness with delay constraints.
short additive quaternary codes. in this paper, the best parameters of quaternary additive codes of small length are determined using the geometric description. only one open question remains for length ≤ 13. among the results obtained in this work are the nonexistence of [12, 7, 5]-codes and [12, 4.5, 7]-codes as well as the existence of a [13, 7.5, 5]-code.
generally explicit space-time codes with nonvanishing determinants for arbitrary numbers of transmit antennas. nonvanishing determinants have emerged as an attractive criterion enabling a space-time code achieve the optimal diversity-multiplexing gains tradeoff. it seems that cyclic division algebras play the most crucial role in designing a space-time code with nonvanishing determinants. in this paper, we explicitly construct space-time codes for arbitrary numbers of transmit antennas that achieve nonvanishing determinants and the optimal diversity-multiplexing gains tradeoff over z[i]. unlike previous methods usually arising a field compositum for two or more fields, our scheme, which only requires one simple extension, constitutes a much more efficient and feasible advancement whether in theory or practice.
on the cusick-cheon conjecture about balanced boolean functions in the cosets of the binary reed-muller code. in this paper, an amplification of the cusick-cheon conjecture on balanced boolean functions in the cosets of the binary reed-muller code rm(k,m) of order k and length 2m, in the cases where k = 1 or k ≥ (m-1)/2, is proved.
detection of gauss-markov random fields with nearest-neighbor dependency. the problem of hypothesis testing against independence for a gauss-markov random field (gmrf) is analyzed. assuming an acyclic dependency graph, an expression for the log-likelihood ratio of detection is derived. assuming random placement of nodes over a large region according to the poisson or uniform distribution and nearest-neighbor dependency graph, the error exponent of the neyman-pearson detector is derived using large-deviations theory. the error exponent is expressed as a dependency-graph functional and the limit is evaluated through a special law of large numbers for stabilizing graph functionals. the exponent is analyzed for different values of the variance ratio and correlation. it is found that a more correlated gmrf has higher exponent at low values of the variance ratio whereas the situation is reversed at high values of the variance ratio.
two new families of optimal binary sequences obtained from quaternary sequences. in this paper, we present two optimal binary families of sequences of length 2n - 1 and 2(2n - 1) for odd integer n. they are obtained as the images of recently proposed optimal quaternary sequences under the most significant bit and the gray maps. the first family has 2n + 1 sequences of length 2n - 1 and the identical correlation distribution to that of gold sequences and gold-like sequences, and the second family of sequences of length 2(2n - 1) has 2n sequences and the same correlation values as those of kerdock sequences.
the construction of variable length codes with good synchronization properties. variable length codes offer advantages for data compression, but are susceptible to loss of synchronization if a bit error occurs. this can be mitigated by the use of variable length codes with specific mechanisms for resynchronization. such mechanisms exist in the codes known as huffman equivalent (he) codes and t-codes. these have been extensively studied in the literature. for optimal compression a length vector is obtained from the probabilities of the symbols of the alphabet used. however, he-codes and t-codes do not exist for all length vectors. in this paper, a new class of variable length codes with good synchronization properties is developed. these are referred to as ordered termination (ot) codes. ot-codes do exist for all length vectors. experimental results and some theoretical support suggest that ot-codes compare favorably with he- and t-codes.
secrecy capacity region of a multiple-antenna gaussian broadcast channel with confidential messages. wireless communication is particularly susceptible to eavesdropping due to its broadcast nature. security and privacy systems have become critical for wireless providers and enterprise networks. this paper considers the problem of secret communication over the gaussian broadcast channel, where a multiple-antenna transmitter wishes to send independent confidential messages to two users with information-theoretic secrecy. that is, each user would like to obtain its own confidential message in a reliable and safe manner. this communication model is referred to as the multiple-antenna gaussian broadcast channel with confidential messages (mgbc-cm). under this communication scenario, a secret dirty-paper coding scheme and the corresponding achievable secrecy rate region are first developed based on gaussian codebooks. next, a computable sato-type outer bound on the secrecy capacity region is provided for the mgbc-cm. furthermore, the sato-type outer bound proves to be consistent with the boundary of the secret dirty-paper coding achievable rate region, and hence, the secrecy capacity region of the mgbc-cm is established. finally, two numerical examples demonstrate that both users can achieve positive rates simultaneously under the information-theoretic secrecy requirement.
code rate-diversity-multiplexing tradeoff. multiple antenna systems can be used to increase system reliability or to increase system capacity. initially, space-time codes were designed to achieve one of these two types of gain. recently, though, a tradeoff between these two system resources has been characterized by the diversity-multiplexing tradeoff. achieving this optimal performance frontier requires proper coding. for diversity optimality, the signal transmitted from each antenna must redundantly describe the message bits. this redundancy has been quantified by the rate of a space-time code, which relates space-time codebook size to constituent single-input-single-output (siso) constellation size. achievable diversity has also been shown to decrease with increasing rates, which establishes the diversity-rate tradeoff. in this work, we consider a generalized notion of the rate of the space-time code, which we refer to as the code rate rc, and the associated diversity-code rate tradeoff. we then generalize the diversity-multiplexing and diversity-code rate tradeoffs and find that a new diversity-multiplexing tradeoff exists as a function of the code rate.
general paradigm for distilling classical key from quantum states. in this paper, we develop a formalism for distilling a classical key from a quantum state in a systematic way, expanding on our previous work on a secure key from bound entanglement (horodecki et. al., 2005). more detailed proofs, discussion, and examples are provided of the main results. namely, we demonstrate that all quantum cryptographic protocols can be recast in a way which looks like entanglement theory, with the only change being that instead of distilling einstein-podolsky-rosen (epr) pairs, the parties distill private states. the form of these general private states are given, and we show that there are a number of useful ways of expressing them. some of the private states can be approximated by certain states, which are bound entangled. thus, distillable entanglement is not a requirement for a private key. we find that such bound entangled states are useful for a cryptographic primitive we call a controlled private quantum channel (pqc). we also find a general class of states, which have negative partial transpose (are npt), but which appear to be bound entangled. the relative entropy distance is shown to be an upper bound on the rate of a key. this allows us to compute the exact value of a distillable key for a certain class of private states.
computing partial walsh transform from the algebraic normal form of a boolean function. we study the relationship between the walsh transform and the algebraic normal form (anf) of a boolean function. in the first part of the paper, we obtain a formula for the walsh transform at a certain point in terms of parameters derived from the algebraic normal form. we use previous results by carlet and guillot to obtain an explicit expression for thewalsh transform at a point in terms of parameters derived from the anf. the second part of the paper is devoted to simplify this formula and develop an algorithm to evaluate it. this algorithm can be applied in situations where it is practically impossible to use the fastwalsh transform algorithm. experimental results show that under certain conditions it is possible to execute our algorithm to evaluate thewalsh transform (at a small set of points) of functions on a few scores of variables having a few hundred terms in the algebraic normal form.
exact characterization of the minimax loss in error exponents of universal decoders. universally achievable error exponents pertaining to certain families of channels (most notably, discrete memoryless channels (dmcs) and various ensembles of random codes, are studied by combining the competitive minimax approach, proposed by feder and merhav, with chernoff bound and gallager's techniques for the analysis of error exponents. in particular, we derive a single-letter expression for the largest, universally achievable fraction ξ of the optimum error exponent pertaining to the optimum maximum-likelihood (ml) decoding. moreover, a simpler single-letter expression for a lower bound to ξ is presented. to demonstrate the tightness of this lower bound, we use it to show that ξ = 1, for the binary symmetric channel (bsc), when the random coding distribution is uniform over: i) all codes (of a given rate), and ii) all linear codes, in agreement with well-known results. we also show that ξ =1 for the uniform ensemble of systematic linear codes, and for that of time-varying convolutional codes in the bit-error-rate sense. for the latter case, we also derive the corresponding universal decoder explicitly and show how it can be efficiently implemented using a slightly modified version of the viterbi algorithm which employs two trellises.
the trapping redundancy of linear block codes. we generalize the notion of the stopping redundancy in order to study the smallest size of a trapping set in tanner graphs of linear block codes. in this context, we introduce the notion of the trapping redundancy of a code, which quantifies the relationship between the number of redundant rows in any parity-check matrix of a given code and the size of its smallest trapping set. trapping sets with certain parameter sizes are known to cause error-floors in the performance curves of iterative belief propagation (bp) decoders, and it is therefore important to identify decoding matrices that avoid such sets. bounds on the trapping redundancy are obtained using probabilistic and constructive methods, and the analysis covers both general and elementary trapping sets. numerical values for these bounds are computed for the [2640,1320] margulis code and the class of projective geometry codes, and compared with some new code-specific trapping set size estimates.