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Information Theory and Applications Workshop, 2008

Date Jan. 27 2008-Feb. 1 2008

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Displaying Results 1 - 25 of 91
  • Author index

    Publication Year: 2008 , Page(s): i - iii
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  • 2008 Information theory and applications workshop

    Publication Year: 2008 , Page(s): c1
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  • Table of contents

    Publication Year: 2008 , Page(s): 1 - 4
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  • 2008 information theory and applications workshop

    Publication Year: 2008 , Page(s): iv
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  • Adaptive rateless coding under partial information

    Publication Year: 2008 , Page(s): 5 - 11
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB) |  | HTML iconHTML  

    We present novel rateless codes that generalize and outperform LT codes (with respect to overall communication and computation complexity) when some input symbols are already available at the decoding host. This case can occur in data synchronization scenarios, or where feedback is provided or can be inferred from transmission channel models. We provide analysis and experimental evidence of this improvement, and demonstrate the efficiency of the new code through implementation on highly constrained sensor devices. View full abstract»

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  • On power-of-choice in downlink transmission scheduling

    Publication Year: 2008 , Page(s): 12 - 17
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    A low-complexity guiding principle is considered for transmission scheduling from n homogeneous queues whose channel states fluctuate independently. The scheduler transmits from a longest queue within d randomly chosen queues with eligible channel states. A Markovian model is studied where mean packet transmission time is n-1 and packet arrival rate is lambda < 1 per queue. Equilibrium distribution of queue occupancy is obtained in the limit as n rarr infin and it is shown to have tails that decay as Theta((lambda/d)k). If transmissions are scheduled from a longest eligible queue in the entire system then almost all queues are empty in equilibrium; the number of queues with one packet is Theta(1) and the number of queues with more than one packet is o(1) as n rarr infin. Equilibrium distribution of the total number of packets in the system is also characterized in this latter case. View full abstract»

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  • Reduction of ML decoding complexity for MIMO Sphere Decoding, QOSTBC, and OSTBC

    Publication Year: 2008 , Page(s): 18 - 25
    Cited by:  Papers (8)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    In this paper, we discuss three applications of the QR decomposition algorithm to decoding in a number of Multi-Input Multi-Output (MIMO) systems. In the first application, we propose a new structure for MIMO Sphere Decoding (SD). We show that the new approach achieves 80% reduction in the overall complexity compared to conventional SD for a 2 times 2 system, and almost 50% reduction for the 4 times 4 and 6 times 6 cases. In the second application, we propose a low complexity Maximum Likelihood Decoding (MLD) algorithm for quasi-orthogonal space-time block codes (QOSTBCs). We show that for N = 8 transmit antennas and 16-QAM modulation scheme, the new approach achieves > 97% reduction in the overall complexity compared to conventional MLD, and > 89% reduction compared to the most competitive reported algorithms in the literature. This complexity gain becomes greater when the number of transmit antennas (N) or the constellation size (L) becomes larger. In the third application, we propose a low complexity Maximum Likelihood Decoding (MLD) algorithm for orthogonal space-time block codes (OSTBCs) based on the real-valued lattice representation and QR decomposition. For a system employing the well-known Alamouti OSTBC and 16-QAM modulation scheme, the new approach achieves > 87% reduction in the overall complexity compared to conventional MLD. Moreover, we show that for square L-QAM constellations, the proposed algorithm reduces the decoding computational complexity from O(LN/2) for conventional MLD to O(L) for systems employing QOSTBCs and from O(L) for conventional MLD to O(radicL) for those employing OSTBCs without sacrificing the performance. View full abstract»

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  • Optimal causal quantization of Markov Sources with distortion constraints

    Publication Year: 2008 , Page(s): 26 - 30
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    For Markov sources, the structure of optimal causal encoders minimizing the total communication rate subject to a mean-square distortion constraint is studied. The class of sources considered lives in a continuous alphabet, and the encoder is allowed to be variable-rate. Both the finite-horizon and the infinite-horizon problems are considered. In the finite-horizon case, the problem is non-convex, whereas in the infinite-horizon case the problem can be convexified under certain assumptions. For a finite horizon problem, the optimal deterministic causal encoder for a kth-order Markov source uses only the most recent k source symbols and the information available at the receiver, whereas the optimal causal coder for a memoryless source is memoryless. For the infinite-horizon problem, a convex-analytic approach is adopted. Randomized stationary quantizers are suboptimal in the absence of common randomness between the encoder and the decoder. If there is common randomness, the optimal quantizer requires the randomization of at most two deterministic quantizers. In the absence of common randomness, the optimal quantizer is non-stationary and a recurrence-based time-sharing of two deterministic quantizers is optimal. A linear source driven by Gaussian noise is considered. If the process is stable, innovation coding is almost optimal at high-rates, whereas if the source is unstable, then even a high-rate time-invariant innovation coding scheme leads to an unstable estimation process. View full abstract»

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  • A note on Kloosterman sums and its application

    Publication Year: 2008 , Page(s): 31 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (190 KB) |  | HTML iconHTML  

    The number of times the trace of a certain function on an extension field assumes a fixed value in the base field is considered. It is shown that the set of all such values enjoys a Fourier transform like property with Kloosterman sums. The application of this property to coding and cryptography is briefly discussed. View full abstract»

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  • Spectrum-blind sampling and compressive sensing for continuous-index signals

    Publication Year: 2008 , Page(s): 547 - 554
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (186 KB) |  | HTML iconHTML  

    Spectrum-blind sampling (SBS), proposed in the mid-90psilas, is a sensing technique enabling minimum-rate sampling and reconstruction of signals with unknown but sparse spectra. SBS is applicable to continuous or discrete-index signals, finite or infinite length, in one or more dimensions. We revisit SBS and explore its relationship to compressive sensing (CS). On the one hand, recent results in CS provide efficient reconstruction techniques for SBS. On the other hand, SBS provides efficient structured designs for blind, non-adaptive sensing of spectrum-sparse signals with minimal sampling requirements, and formulation leading to reconstruction cost only linear in the amount of data, and robustness against noise. View full abstract»

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  • Isoperimetrically Pareto-optimal shapes on the hexagonal grid

    Publication Year: 2008 , Page(s): 507 - 522
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (337 KB) |  | HTML iconHTML  

    In the plane, the way to enclose the most area with a given perimeter and to use the shortest perimeter to enclose a given area, is to use a circle. If we replace the plane by a regular tiling of it, and construct polyforms i.e. shapes as sets of tiles, things become more complicated. We need to redefine the area and perimeter measures, and study the consequences carefully. In this paper we characterize all shapes that have both shortest boundaries and maximal areas for one particular boundary measure on the hexagon tiling. We show this set of Pareto optimal shapes is the same as that induced by a different boundary measure that was studied in the context of theoretical chemistry. View full abstract»

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  • Feedback schemes for multiuser MIMO-OFDM downlink

    Publication Year: 2008 , Page(s): 33 - 40
    Cited by:  Papers (1)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    We consider a MIMO-OFDM broadcast channel and compare achievable ergodic rates under three channel state feedback schemes: analog feedback, direction quantized feedback and ldquotime-domainrdquo channel quantized feedback. The third scheme is new, and it is inspired by rate-distortion theory of Gaussian correlated sources. For each scheme we derive the conditions under which the system achieves full multiplexing gain. The first two schemes are direct extensions of previously proposed schemes to the OFDM case. The key difference with respect to the widely treated frequency-flat case is that in MIMO-OFDM the ldquofrequency-domainrdquo channel is a Gaussian correlated source. The new ldquotime-domainrdquo quantization scheme takes advantage of the channel frequency correlation structure and outperforms the other schemes. Furthermore, it is by far simpler to implement than complicated spherical vector quantization. In particular, we observe that no structured codebook design and vector quantization is actually needed for efficient channel state information feedback. View full abstract»

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  • Can the storage capacity of memories built from unreliable components be determined?

    Publication Year: 2008 , Page(s): 41 - 43
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    A memory is a device in which information is stored at some time and retrieved at a later time . Let the information be stored in form of bits in registers (memory elements) each of which can store a single bit. The information storage capability of a memory is the number of information bits it stores. Building a memory with information storage capability of k bits with reliable memory elements requires k registers. Such a memory is termed as an irredundant memory. This paper considers the problem of building a memory with memory elements and logic gates which fail according to a known random mechanism. The required minimum redundancy memory in which makes arbitrarily reliable information possible is discussed. For a reliable storage, the information needs to be stored in coded form . To ensure reliability, a correcting circuit is employed which performs error correction and updates the contents of the registers with an estimate of the original codeword. View full abstract»

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  • Information rates for multiantenna systems with unknown fading

    Publication Year: 2008 , Page(s): 44 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    This work first presents a general technique to compute tight upper and lower bounds on the information rate of a multiuser Rayleigh fading channel with no channel state information (CSI) at the transmitters or the receivers. The paper then presents analytical upper and lower bounds on the information rate which converge in the limit of large number of transmitting users where the channel bandwidth is large compared to the user data rates, e.g., when users can employ CDMA. In this limit, the capacity (per Hz) of the individual users is decreasing while the sum capacity (per Hz) is constant. The paper concludes with exact analytical expressions for the information rates of both the block fading and the continuous correlated fading channel models in this regime. View full abstract»

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  • On the single-slot capacity of random access over a Gaussian MAC

    Publication Year: 2008 , Page(s): 50 - 53
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (229 KB) |  | HTML iconHTML  

    Consider a Gaussian multiple access channel (MAC) with two users, which do not always have a message to transmit. Neither user knows if the other is transmitting or not. Each user has two possible achievable rates depending on whether the other user is transmitting or not. Hence, in general, any coding scheme is characterized by a 4-tuple of rates. For given power constraints, we prove inner and outer bounds to the (4-dimensional) capacity region. View full abstract»

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  • Ergodic capacity maximizing MIMO ARQ precoder design based on channel mean information

    Publication Year: 2008 , Page(s): 58 - 62
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB) |  | HTML iconHTML  

    In recent years, there has been broad research interest in the development of beamforming and precoding techniques for MIMO wireless communication systems. Most existing works focus on the single transmission session between transceivers. We expand the MIMO precoder design to take into account the significant role that ARQ (Automatic Repeat reQuest) may play in practical systems. We investigate the design of linear precoders for maximizing the ergodic capacity of MIMO-ARQ systems. Without the precise channel knowledge, our low complexity precoder designs are based on MIMO channel statistic information to achieve significant performance gain under ARQ. View full abstract»

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  • Asymptotic ensemble enumerators for protograph-based generalized LDPC codes: Computational complexity

    Publication Year: 2008 , Page(s): 63 - 65
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (157 KB) |  | HTML iconHTML  

    In earlier work, we presented a method for finding ensemble weight enumerator for protograph-based generalized LDPC (G-LDPC) codes, and leveraged this method to find ensemble stopping set enumerator and ensemble trapping set enumerator. The method is conceptually simple, but when the dimensionality of the constraint nodes (number of their code-words) grows, it becomes difficult to handle the computational complexity, which rise while evaluating these enumerators. To deal with this difficulty, we posed a conjecture, which greatly reduce the computational complexity. Trails to proof this conjecture showed that the proof is a challenging problem. Also, proving it will strengthen the theory of enumerating protograph-based G-LDPC code ensembles. Which in turn helps in predicating the average performances for codes drawn from these ensembles. In Section II we present a review of our method for finding finite and asymptotic weight enumerators for protograph-based G-LDPC code ensembles. Then, we present the conjecture in Section III with some examples. View full abstract»

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  • Buffering requirements for variable-iterations LDPC decoders

    Publication Year: 2008 , Page(s): 523 - 530
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (438 KB) |  | HTML iconHTML  

    Low-density parity-check (LDPC) decoders, like iterative decoders for other block codes, can be designed to stop after a variable number of iterations, dependent on the difficulty of decoding particular noisy received words, also called frames. The number of iterations the decoder spends on a given frame determines both the probability of successful decoding, and the time expended. But whereas the speed of an LDPC decoder without a buffer is determined by its most difficult frames, the speed of a variable-iterations decoder with sufficient buffering approaches that determined by frames of average difficulty. It is relatively straightforward to analyze this as a D/G/1 queuing problem combined with empirically measured probability distributions of iteration counts for specific LDPC codes. Our analysis parallels that of other researchers, e.g., (J. Vogt and A. Finger, 2001), (G. Bosco et al., 2005), (M. Rovini and A. Martinez, 2007), and examines the resulting implications on LDPC decoder design choices. We find that a buffer large enough to hold only B = 2 or 3 additional frames is sufficient to achieve near optimal performance. We prove a strong monotonicity condition: not only does a variable-iterations decoder with buffer size B +1 frames outperform one with buffer size B in terms of average error rate, every single frame is guaranteed to receive at least as many iterations from the decoder with the larger buffer, if needed. Significantly, at low error rates, a variable-iterations decoder with buffer size B can keep pace with an input data rate B +1 times faster than a fixed-iterations decoder with the same processing speed. View full abstract»

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  • A note on convergence rate of constrained capacity estimation algorithms over ISI channels

    Publication Year: 2008 , Page(s): 66 - 69
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB) |  | HTML iconHTML  

    It has recently become popular to use simulation-based algorithms to empirically estimate achievable information rates over intersymbol interference (ISI) channels with inputs from specific input constellations. Such algorithms are guaranteed to converge by invoking the Shannon-McMillan-Brieman theorem provided that the output sequence is stationary and ergodic. In this note, we establish a central limit theorem result on the rate of convergence, and show that the variance of the estimates decreases like 1/N (where N is the sequence length employed) as N goes to infinity. This result indicates that it is possible to achieve estimation accuracy with any desired level by simply increasing the number of samples appropriately. View full abstract»

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  • Optimal multiple description and multiresolution scalar quantizer design

    Publication Year: 2008 , Page(s): 70 - 76
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB) |  | HTML iconHTML  

    The author presents new algorithms for fixed-rate multiple description and multiresolution scalar quantizer design. The algorithms both run in time polynomial in the size of the source alphabet and guarantee globally optimal solutions. To the authorpsilas knowledge, these are the first globally optimal design algorithms for multiple description and multiresolution quantizers. View full abstract»

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  • Spectra and minimum distances of repeat multiple accumulate codes

    Publication Year: 2008 , Page(s): 77 - 86
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (326 KB) |  | HTML iconHTML  

    In this paper we consider ensembles of codes, denoted RAm, obtained by a serial concatenation of a repetition code and m accumulate codes through uniform random inter-leavers. We analyze their average spectrum functions for each m showing that they are equal to 0 below a threshold distance isinm and positive beyond it. One of our main results is to prove that these average spectrum functions form a not-increasing sequence in m converging uniformly to a limit spectrum function which is equal to the maximum between the average spectrum function of the classical linear random ensemble and 0. As a consequence the sequence isinm converges to the Gilbert-Varshamov distance. A further analysis allows to conclude that the threshold distance isinm is indeed the typical distance of the ensemble RAm when the interleaver length goes to infinity. Combining the two results we are able to conclude that the typical distance of the ensembles RAm converges to the Gilbert-Varshamov bound. View full abstract»

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  • On the throughput of acyclic wired packet networks with finite buffers

    Publication Year: 2008 , Page(s): 87 - 93
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (250 KB) |  | HTML iconHTML  

    In this paper, we study the effect of finite buffer sizes on the (unicast) throughput in directed acyclic wired erasure networks. First, we motivate the problem by presenting the underlying idea of throughput estimation in wireline networks. We observe that the problem of exact throughput estimation for wireline networks is equivalent to the calculation of steady state probabilities for a regular, ergodic Markov chain. We extend the ideas of rate loss and information leakage due to buffer overflow (i.e., discarding of packets) at nodes to general wired acyclic packet networks. We then use the estimates of the loss in rate at various nodes to derive simple and easily estimable bounds on the maximum achievable rate of information transmission during unicast sessions in such networks. View full abstract»

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  • On information theoretic aspects of single- and multi-carrier communications

    Publication Year: 2008 , Page(s): 94 - 99
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (359 KB) |  | HTML iconHTML  

    In this paper, we investigate the relation between the quadrature amplitude modulation (QAM) input information rates (IRs) of multi-carrier (MC) and single carrier (SC) systems transmitted over inter-symbol interference (ISI) channels with additive white Gaussian noise (AWGN). In particular, considering uniform power spectrum transmission, we conjecture that, for a given channel impulse response, the IR corresponding to an SC input distribution is higher than that corresponding to an MC input distribution. We give an intuitive justification of our conjecture and confirm it, by means of numerical results, considering two sets of randomly generated channels. View full abstract»

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  • Dynamic decentralized multi-channel MAC protocols

    Publication Year: 2008 , Page(s): 100 - 110
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (367 KB) |  | HTML iconHTML  

    In this paper, we propose new dynamic decentralized multi-channel multiple access (MAC) protocols and study their performance. Our protocols build on slotted Aloha, but extend it in several ways to improve flow completion time and throughput, as follows: (i) channels are assigned to flows rather than packets to eliminate per packet collisions, thus the total number of collisions is reduced, and (ii) each flow owns or drops channels dynamically considering successful transmissions, thus the number of owned channels adapts to varying traffic. We present an analysis of the stability region and of flow completion times, for our algorithms, and show that one of them can achieve close to 100% throughput if flow sizes are large. We demonstrate by extensive simulations that, compared to current multi-channel MAC protocols, our algorithms improve flow completion time and throughput in wireless local area and mesh networks. View full abstract»

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  • The pre-log of Gaussian broadcast with feedback can be two

    Publication Year: 2008 , Page(s): 545 - 546
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (218 KB) |  | HTML iconHTML  

    A generic intuition says that the pre-log, or multi-plexing gain, cannot be larger than the minimum of the number of transmit and receive dimensions. This suggests that for the scalar broadcast channel, the pre-log cannot exceed one. By contrast, in this note, we show that when the noises are anti-correlated and feedback is present, then a pre-log of two can be attained. In other words, in this special case, in the limit of high SNR, the scalar Gaussian broadcast channel turns into two parallel AWGN channels. Achievability is established via a coding strategy due to Schalkwijk, Kailath, and Ozarow. View full abstract»

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