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Information Theory Workshop, 2004. IEEE

Date 24-29 Oct. 2004

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Displaying Results 1 - 25 of 97
  • Grammar-based coding: new perspectives

    Publication Year: 2004 , Page(s): 105 - 110
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (770 KB) |  | HTML iconHTML  

    Grammar-based coding is investigated from three new perspectives. First, we revisit the performance analysis of grammar-based codes by proposing context-based run-length encoding algorithms as new performance benchmarks. A redundancy result stronger than all previous corresponding results is established. We then extend the analysis of grammar-based codes to sources with countably infinite alphabets. Let Λ denote an arbitrary class of stationary, ergodic sources with a countably infinite alphabet. It is shown that grammar-based codes can be modified so that they are universal with respect to any Λ for which there exists a universal code. Moreover, upper bounds on the worst-case redundancies of grammar-based codes among large sets of length-n individual sequences from a countably infinite alphabet are established. Finally, we propose a new theoretic framework for compression in which grammars rather than sequential stochastic processes are used as source generating models, and point out some open problems in the framework. View full abstract»

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  • Design of sensor networks for detection applications via large-deviation theory

    Publication Year: 2004 , Page(s): 153 - 158
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (666 KB) |  | HTML iconHTML  

    This paper outlines interesting applications of large-deviation theory and asymptotic analysis to the design of wireless sensor networks. Sensor networks are envisioned to contain a large amount of wireless nodes. As such, asymptotic regimes where the number of nodes becomes large are important tools in identifying good design rules for future sensor systems. Through a simple example, we show how the Gartner-Ellis theorem can be used to study the impact of density on overall performance in resource constrained systems. Specifically, we consider the problem where sensor nodes receive partial information about their environment, and then send a summary of their observations to a fusion center for the purpose of detection. Each node transmits its own data on a noisy communication channel. Observations are assumed to become increasingly correlated as sensor nodes are placed in close proximity. It is found that high node density performs well even when observations from adjacent sensors are highly correlated. Furthermore, the tools presented in this paper can be employed for a more complete analysis of the tradeoff between resource allocation, system complexity, and overall performance in wireless sensor networks. View full abstract»

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  • Zero-error information and applications in cryptography

    Publication Year: 2004 , Page(s): 1 - 6
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (697 KB) |  | HTML iconHTML  

    In analogy to the zero-error variant of the channel capacity, the zero-error information between two random variables is defined. We show that our definition is natural in the sense that the representation of the channel capacity with respect to mutual information carries over to the zero-error variants of the quantities. It is shown that the new notion, together with two operators introduced in the same context, namely the common random variable of two random variables and the dependent part of a random variable with respect to another, is useful for giving characterizations of the possibility of realizing cryptographic tasks - such as bit commitment, coin tossing, or oblivious transfer - from correlated pieces of information. View full abstract»

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  • Capacity bounds for an ultra-wideband channel model

    Publication Year: 2004 , Page(s): 176 - 181
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (655 KB) |  | HTML iconHTML  

    There is an ongoing effort by the IEEE 802.15.3a subcommittee to reach a UWB personal area network standard. We estimate the achievable rates for such networks using a channel model specified by the same group. The analysis of this channel model is of interest in light of recent information-theoretic work on multipath fading channels which show that in order to take full advantage of such channels' capacity the transmitted signals have to be "peaky" in a certain sense. The immense bandwidth of the UWB channel also suggests at first that peaky signals should be used. However, unlike the many other wireless systems where the transmitter energy is limited, in the UWB channel only the power spectral density of the transmitted signal is constrained. As a result, the signal power can grow in proportion to the utilized bandwidth and peaky signals are not needed. View full abstract»

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  • Decentralized network coding

    Publication Year: 2004 , Page(s): 310 - 314
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (698 KB) |  | HTML iconHTML  

    This paper proposes deterministic algorithms for decentralized network coding. Decentralized coding allows us to locally specify the coding operations at network nodes without knowledge of the overall network topology, and to accommodate future changes in the network such as addition of receivers. To the best of our knowledge, these are the first deterministic decentralized algorithms proposed for network coding. View full abstract»

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  • Enumeration algorithms for constructing (d1, ∞, d2, ∞) run length limited arrays: capacity estimates and coding schemes

    Publication Year: 2004 , Page(s): 141 - 146
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (614 KB) |  | HTML iconHTML  

    We present two enumeration algorithms for a class of (d1, ∞, d2, ∞) run-length limited (RLL) constrained arrays. Based on the structure of these algorithms, we derive bounds for the maximum information rate of the constraint. We also give encoders and decoders for coded 2D constrained arrays with rates close to the derived bounds. View full abstract»

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  • A concatenated [(4, 1, 3)] quantum convolutional code

    Publication Year: 2004 , Page(s): 28 - 33
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (668 KB) |  | HTML iconHTML  

    We construct a concatenated [(4, 1, 3)] quantum convolutional code from a (2, 1, 2) classical convolutional code. This quantum convolutional code can correct one general error. View full abstract»

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  • Combining data fusion with joint source-channel coding of correlated sensors

    Publication Year: 2004 , Page(s): 315 - 317
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (526 KB) |  | HTML iconHTML  

    We consider a source sensed by several correlated sensors. Each one of the sensors receives a noisy version of the source, performs channel coding, and transmits this information through an independent noisy channel to a central processing unit. The processing unit fuses all the received sequences with the objective of obtaining the best possible estimate of the source of interest. This is performed by utilizing at the decoder a graphical model that jointly describes the channel decoders for each sensor and the probabilistic dependence between the source and the sensors. View full abstract»

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  • On the variable-delay reliability function of discrete memoryless channels with access to noisy feedback

    Publication Year: 2004 , Page(s): 336 - 341
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (737 KB) |  | HTML iconHTML  

    We give a scheme for variable-delay reliable communication over a noisy discrete memoryless channel with a noisy feedback DMC being available between the receiver and the transmitter. This scheme works when the capacity of the feedback channel is greater than the capacity of the forward channel and the target rate of communication on the forward channel is less than its capacity. Rather than looking at a single block in isolation, we consider the scenario where we expect this system to carry an infinite stream of packets. We show that in the limit of nearly noiseless feedback channels, we approach the Burnashev bound on the reliability of variable-delay channel codes. View full abstract»

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  • Mutual information and conditional mean estimation in Poisson channels

    Publication Year: 2004 , Page(s): 265 - 270
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB) |  | HTML iconHTML  

    Following the recent discovery of new connections between information and estimation in Gaussian channels, this paper reports parallel results in the Poisson regime. Both scalar and continuous-time Poisson channels are considered. It is found that, regardless of the statistics of the input, the derivative of the input-output mutual information with respect to the dark current can be expressed in the expected difference between the logarithm of the input and the logarithm of its conditional mean estimate (noncausal in case of continuous-time). The same is true for the derivative with respect to input scaling, but with the logarithmic function replaced by x log x. View full abstract»

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  • Sensing capacity for target detection

    Publication Year: 2004 , Page(s): 147 - 152
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (719 KB) |  | HTML iconHTML  

    We define a notion of 'sensing capacity' that characterizes the ability of a sensor network to successfully distinguish among a discrete set of targets. Sensing capacity is defined as the maximum ratio of target positions to sensors for which inference of targets within a certain distortion is achievable. We demonstrate a lower bound on this capacity. Unlike previous work on 'sensor network capacity', our notion of sensing capacity is defined by the sensing task itself, as opposed to external resource constraints such as power, communications, and processing. View full abstract»

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  • Two-dimensional error correcting codes using finite-field wavelets

    Publication Year: 2004 , Page(s): 22 - 27
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (699 KB) |  | HTML iconHTML  

    This paper introduces two-dimensional wavelet codes (TDWC). First, we study the encoder of half-rate TDWC. We show that these linear codes are lattice-cyclic. We prove that any two-dimensional lattice-cyclic code can also be generated by a two-dimensional wavelet transform. Second, we introduce a methodology to design TDWC over binary erasure channels. We show that the half-rate TDWC of dimensions N1 × N2 can recover burst erasures of size up to N1 × N2/2 and N1/2 × N2, and N2/2 × N2. Finally, we present examples of TDWC that satisfy the Reiger bound with equality (capable of correcting any burst of size (N1N2)/2). Since these codes are lattice-cyclic, their erasure decoding can be simplified. View full abstract»

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  • Capacity, stability and flows in large-scale random networks

    Publication Year: 2004 , Page(s): 159 - 164
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB) |  | HTML iconHTML  

    We consider the problem of determining the maximum stable throughput in large-scale random networks under a fairness constraint. The networks are modeled as random unit-disk graphs, and the problem of throughput stability is formulated as one finding the maximum value of a multicommodity flow problem. In this paper, we construct upper and lower bounds on the value of that multicommodity flow problem which, together, provide a tight characterization of an optimal solution to within constants independent of network size. These results contain as a special case those of Gupta and Kumar for random networks, for which an entirely new derivation is provided, using only elementary counting and discrete probability tools. View full abstract»

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  • Extremal distributions in information theory and hypothesis testing

    Publication Year: 2004 , Page(s): 76 - 81
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (729 KB) |  | HTML iconHTML  

    Many problems in information theory can be distilled to an optimization problem over a space of probability distributions. The most important examples are in communication theory, where it is necessary to maximize mutual information in order to compute channel capacity, and the classical hypothesis testing problem in which an optimal test is based on the maximization of divergence. Two general classes of optimization problems are considered in this paper: convex and linear programs, where the constraint set is defined by a finite number of moment constraints. View full abstract»

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  • Digital fountains: a survey and look forward

    Publication Year: 2004 , Page(s): 271 - 276
    Cited by:  Papers (58)  |  Patents (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (799 KB) |  | HTML iconHTML  

    We survey constructions and applications of digital fountains, an abstraction of erasure coding for network communication. Digital fountains effectively change the standard paradigm where a user receives an ordered stream of packets to one where a user must simply receive enough packets in order to obtain the desired data. Obviating the need for ordered data simplifies data delivery, especially when the data is large or is to be distributed to a large number of users. We also examine barriers to the adoption of digital fountains and discuss whether they can be overcome. View full abstract»

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  • Information theory and coding problems in genetics

    Publication Year: 2004 , Page(s): 60 - 65
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    The aim of this paper is to describe a new class of problems and some new results in coding theory arising from the analysis of the composition and functionality of the genetic code. The major goal of the proposed work is to initiate research on investigating possible connections between the regulatory network of gene interactions (RNGI) and the proofreading (error-control) mechanism of the processes of the central dogma of genetics. New results include establishing a direct relationship between Boolean network (BN) models of RNGI and Gallager's LDPC decoding algorithms. The proposed research topics and described results are expected to have a two-fold impact on coding theory and genetics research. Firstly, they may provide a different setting in which to analyze standard LDPC decoding algorithms, by using dynamical systems and Boolean function theory. Secondly, they may be of use in establishing deeper relationships between the DNA proofreading mechanism, RNGI, and their joint influence on the development and possible treatment of genetic diseases like cancer. View full abstract»

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  • On error exponents of nested lattice codes for the AWGN channel

    Publication Year: 2004 , Page(s): 348 - 352
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    We present a new lower bound for the error exponents of nested lattice codes for the additive white Gaussian noise (AWGN) channel. The exponents are closely related to those of an unconstrained additive noise channel where the noise is a weighted sum of a white Gaussian and a spherically uniform random vector. The new lower bound improves the previous result derived by Erez and Zamir (2002) and stated in terms of the Poltyrev exponents. More surprisingly, the new lower bound coincides with the random coding error exponents of the optimal Gaussian codes for the AWGN channel in the nonexpurgated regime. One implication of this result is that minimum mean squared error (MMSE) scaling, despite its key role in achieving capacity of the AWGN channel, is no longer fundamental in achieving the best error exponents for rates below channel capacity. These exponents are achieved using a lattice inflation parameter derived from a large-deviation analysis. View full abstract»

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  • On multiple description source coding with decoder side information

    Publication Year: 2004 , Page(s): 88 - 93
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (718 KB) |  | HTML iconHTML  

    We formulate a multi-terminal source coding problem, where we are required to construct a multiple-description code for a source sequence when side information about dependent random processes is available at the decoder only, or at both the decoder and the encoder. We describe an achievable rate-distortion region for these problems in two cases: where there is common side-information at the decoders and when they are different. In the quadratic Gaussian case, and when there is common side information among the decoders, we show that the rate region when both the encoder and decoder have access to the side information coincides with that of decoder-only side information. This is analogous to the single-description (Wyner-Ziv) case, and an explicit characterization of the rate-distortion region is provided for this case. View full abstract»

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  • Capacity analysis of MIMO systems with unknown channel state information

    Publication Year: 2004 , Page(s): 413 - 417
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (638 KB) |  | HTML iconHTML  

    We consider a mobile wireless communication system composed of M transmit and N receive antennas operating in a fading environment. Assuming channel state information is unavailable to the transmitter and the receiver, a capacity upper bound of the unknown MIMO channel under the assumption of restricted input distributions is provided. By analyzing the proposed capacity upper bounds, we reinforce the advantages of using an orthogonal pilot structure which minimizes the mean square estimation error, in that it also maximizes the capacity upper bounds. Interestingly, the capacity upper bound is shown to be a monotonically decreasing function with respect to the number of pilot symbols, Tτ. Numerical evaluations of the capacity upper bound further demonstrate that the capacity gain is insignificant when Tτ decreases below M, suggesting an optimum training duration of M time slots. View full abstract»

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  • On the asymptotic performance of threshold-based acquisition systems in multipath fading channels

    Publication Year: 2004 , Page(s): 170 - 175
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (695 KB) |  | HTML iconHTML  

    In this paper, we investigate the asymptotic performance of threshold-based timing acquisition systems having fixed dwell time in multipath fading channels. We show that if the system involves the comparison of a decision statistic to a threshold in order to detect the true symbol timing, then it may not be possible to make the average probability of error in acquisition arbitrarily small, even if the signal-to-noise ratio increases without bound. View full abstract»

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  • On the total weighted square correlation minimization in multicellular synchronous DS-CDMA systems

    Publication Year: 2004 , Page(s): 39 - 44
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (705 KB) |  | HTML iconHTML  

    A definition of total weighted square correlation (TWSC) for an overloaded multicellular synchronous DS-CDMA system in the presence of multipath on the uplink is introduced. We assume the channel state information is known perfectly both at transmitter and receiver. The optimum solutions for minimizing TWSC are the orthogonal generalized WBE (Welch bound equality) spreading sequences. The design of such sequences in the context of cooperative multibase DS-CDMA systems under the TWSC criterion is presented. View full abstract»

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  • Channel symmetry in Slepian-Wolf code design based on LDPC codes with application to the quadratic Gaussian Wyner-Ziv problem

    Publication Year: 2004 , Page(s): 129 - 134
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (758 KB) |  | HTML iconHTML  

    We consider Slepian-Wolf code design (or source coding with side information) based on LDPC codes. We show that density evolution defined in conventional channel coding can be used in analyzing the Slepian-Wolf coding performance provided that a certain symmetry condition, dubbed dual symmetry, is satisfied by the hypothetical channel between the source and the side information. Exploiting such an analysis. we design an efficient LDPC code based Slepian-Wolf coding scheme and apply it to the quadratic Gaussian Wyner-Ziv problems. View full abstract»

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  • Results on punctured LDPC codes

    Publication Year: 2004 , Page(s): 215 - 219
    Cited by:  Papers (18)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (685 KB) |  | HTML iconHTML  

    In this paper we study some fundamental properties of punctured LDPC codes. We first prove that for any ensemble of LDPC codes, there exists a puncturing threshold p*. We then find lower bounds on the achievable rates of punctured codes over general MBIOS channels. These bounds are satisfied by using only one encoder and decoder for all rates. We then prove that for any rates R1 and R2 satisfying 0 < R1 < R2 < 1, there exists an ensemble of LDPC codes with the following property. The ensemble can be punctured from rate R1 to R2 resulting in asymptotically good codes for all rates R1 ≤ R ≤ R2. Specifically, this implies that rates arbitrarily close to one are achievable via puncturing. We also show that punctured LDPC codes are as good as ordinary LDPC codes. For binary erasure channel (BEC) and arbitrary positive numbers R1 < R2 < 1, we prove the existence of the sequences of punctured LDPC codes that are capacity achieving for all rates R1 ≤ R ≤ R2. Based on the above observations, we then propose a method to design good punctured LDPC codes over a broad range of rates. The method is very simple and does not suffer from the performance degradation at high rates. Finally, we show that punctured codes might be useful for proof of the existence of capacity-achieving LDPC codes over memoryless binary-input output-symmetric channels. View full abstract»

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  • On multiple access for distributed dependent sources: a content-based group testing approach

    Publication Year: 2004 , Page(s): 298 - 303
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (735 KB) |  | HTML iconHTML  

    In this paper we consider the multiple access problem with distributed dependent sources. We derive the optimal designs for the case of N correlated binary sources whose data is modelled as a two-state Markov chain. The solution can be classified as a group testing technique where data values at the sensors are determined through the successive refinements of the tests over smaller groups. The tests form, progressively, an accurate map of the sensor data at the central receiver. We derive the conditions on the parameters of the data model for which the group testing approach is superior to time sharing. In contrast to standard multiple access techniques, this is the first method proposed for data retrieval from distributed dependent sources which is content-based rather than user-based. View full abstract»

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  • Broadcasting with fidelity criteria

    Publication Year: 2004 , Page(s): 342 - 347
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB) |  | HTML iconHTML  

    Consider the problem of broadcasting an i.i.d. source sequence X = {Xi} i=1N (possibly N → ∞) to n listeners over a discrete broadcast channel, consisting of n channels with capacities C1 = Cmax ≥ C2 ≥...≥ Cn = Cmin. Let the tuple D = (D1, D2,...,Dn) represent the average distortion in reconstructing sources at the n listeners. The problem of characterizing all achievable tuples D is still open for a general case. For a fairly general class of discrete channels, we prove the achievability of the tuple n(ρ12,...,ρn) = (DX1C1 ζ), DX2C2 - ζ),...,DXnCn - ζ)), provided that λi = (ρiCi - ρi+1Ci+1)/Ci > 0, for 1 ≤ i ≤ n $1, λn = ρn and Σi=1n-1 λi ≤ 1, where DX (R) is the distortion rate function of X. The penalty term ζ = 1/2 for a general source with real alphabets and is ζ = 0 if X is progressively refinable. The factor 0 < ρi ≤ 1 is called the utilization of the ith channel. As an example, for n = 2, we show that 2(1/(2 - C2/C1), 1/(2 $C1/C2)) is achievable for any C1, C2. Furthermore, the common utilization of ρ = (1 + ln(Cmax/Cmin))-1 is shown to be achievable for all channels. Conversely, we find examples of channels, namely erasure switch-to-talk channels, for which the proposed achievable utilizations are tight. In particular, while 3 (2/3, 2/3, 2/3) is achievable for any compatible broadcast channel with capacities C1 = 2C2 = 2C3, for any δ > 0, we find examples of channels for which 3(2/3+δ,2/3+δ,2/3+ δ) is not achievable. View full abstract»

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