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Information Theory Workshop, 2003. Proceedings. 2003 IEEE

Date 31 March-4 April 2003

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Displaying Results 1 - 25 of 90
  • Replica analysis of large-system CDMA

    Page(s): 22 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB) |  | HTML iconHTML  

    We present some new results on large-system CDMA obtained through the replica method developed in statistical physics. We find the spectral efficiency of randomly spread CDMA subject to Gaussian noise and flat fading in the large-system limit under arbitrary input distributions. Both joint decoding and single-user decoding are considered. In the latter case, a conditional mean estimator is first applied to separate the users and it is found that the resulting single-user channel for every user is equivalent to a Gaussian channel. The multiuser efficiency of that Gaussian channel is the same for all users and satisfies a fixed-point equilibrium equation. The additive decomposition by Shamai-Verdu of optimum capacity in terms of single-user capacity is shown to hold for arbitrary input distributions. View full abstract»

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  • Performance analysis of a class of multistage DS-CDMA receivers for multipath channels

    Page(s): 30 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    Performance of the output signal-to-interference-plus-noise ratios (SINRs) and bit error rates (BERs) of the maximum ratio combining (MRC) multistage minimum-mean squared error (MMSE), minimum output energy (MOE), best linear unbiased estimator (BLUE) and maximum likelihood (ML) receivers are analyzed for direct-sequence code-division multiple access (DS-CDMA) systems in multipath Rayleigh fading channels, based on the common multistage structure we proposed previously (Sau-Hsuan Wu et al., Proc. IEEE Globecom, 2002, 2003; Proc. IEEE ICC, 2003). The SINRs of these receivers are proved to be monotonically increasing with the number of applied stages. The upper bound of output SINRs and its achievability conditions are also provided, which are shown to form the condition for the occurrence of BER floors of the multistage MRC MMSE/MOE/BLUE/ML multiuser receivers. A rule for selecting the number of stages is thus provided to take full advantage of the multistage structure of these receivers. View full abstract»

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  • Cooperative space-time coding for wireless networks

    Page(s): 50 - 53
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB) |  | HTML iconHTML  

    We consider a cooperative system in which the partnering mobiles are equipped with multiple antennas. We present space-time codes that have the capability of providing full cooperation diversity, while achieving maximum possible diversity and best performance in the inter-user channel. Our codes also perform well when cooperation does not take place. We illustrate that cooperative space-time coding offers significant performance improvement over direct transmission even when the inter-user channel is noisy. We also consider code design for users with different numbers of antennas. View full abstract»

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  • Information hiding by coverings

    Page(s): 151 - 154
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB) |  | HTML iconHTML  

    We propose a formal model for embedding information in black and white images and prove the equivalence between the existence of embedding schemes and covering codes. An asymptotically tight bound on the performance of embedding schemes is given. We construct efficient embedding schemes via known coverings. In particular, one of those schemes allows the embedding of up to log2(n+1) bits in coverwords of n bits, changing at most one bit, which is twice as good as the scheme of Y.-Y. Chen et al. (see Proc. IEEE Symp. on Computers and Communication - ISCC 2000, p.750-5, 2000). We rewrite some previous schemes with a look towards their covering structures. Finally, we address the problem of active warden in a similar way, giving a model, establishing the relationship with centered codes and concluding by a construction of schemes resistant to active warden. View full abstract»

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  • Approaching near-capacity on a multi-antenna channel using multirate encoding and successive decoding receivers

    Page(s): 54 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB) |  | HTML iconHTML  

    We address the problem of designing multirate codes for a multiple-input and multiple-output (MIMO) system by restricting the receiver to be a successive decoding and interference cancellation type, when each of the input signals is encoded independently. It is assumed that the receiver knows the instantaneous fading channel states but the transmitter does not have access to them. We design a multirate coded MIMO system using punctured turbo codes and demonstrate the efficiency of the proposed scheme using simulation results. In particular, the simulation results show performance within 2 dB of MIMO channel capacity. View full abstract»

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  • A new identity based signcryption scheme from pairings

    Page(s): 155 - 158
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (518 KB) |  | HTML iconHTML  

    We present a new identity based scheme using pairings over elliptic curves. It combines the functionalities of signature and encryption and is provably secure in the random oracle model. We compare it with J. Malone-Lee's scheme from the points of view of security and efficiency. We give a proof of semantic security under the decisional bilinear Diffie-Hellman assumption for this new scheme. View full abstract»

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  • An algorithm for cycle and add property of m-sequence

    Page(s): 119 - 122
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB) |  | HTML iconHTML  

    The cycle and add properties (CAP) of m-sequences are discussed. For given integers τ and η, a method which decides λ to satisfy the CAP {ak+η}+{ak+τ}={ak+λ} is proposed; the acquisition of the CAP of an m-sequence, {ak}, only depends on the reciprocal polynomial of the primitive polynomial which produces the m-sequence and the cyclotomic cosets mod pn-1. View full abstract»

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  • Low-complexity near-maximum-likelihood detection and precoding for MIMO systems using lattice reduction

    Page(s): 345 - 348
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (501 KB) |  | HTML iconHTML  

    We consider the lattice-reduction-aided detection scheme for 2×2 channels recently proposed by H. Yao and G.W. Wornell (see Proc. IEEE Globecom, 2002). By using an equivalent real-valued substitute MIMO channel model, their lattice reduction algorithm can be replaced by the well-known LLL (Lenstra-Lenstra-Lovasz) algorithm (Lenstra, A.K. et al., 1982), which enables the application of the algorithm to MIMO systems with arbitrary numbers of dimensions. We show how lattice reduction can also be favourably applied in systems that use precoding and give simulation results that underline the usefulness of this approach. View full abstract»

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  • Lower bounds on the existence of binary error-correcting variable-length codes

    Page(s): 300 - 303
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (509 KB) |  | HTML iconHTML  

    The paper deals with codes that combine source and channel encoding operations. After discussing the potential usefulness of these variable-length error correcting (VLEC) codes, necessary conditions on their length distribution are established. It is shown that, depending on the targetted application, several families of VLEC codes can be defined, whose conditions of existence differ. View full abstract»

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  • Improved signal design for bandwidth efficient multiple access

    Page(s): 34 - 37
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (514 KB) |  | HTML iconHTML  

    The problem of optimizing signals for the Gaussian multiple access channel under a quality of service (QoS) constraint is addressed. In particular, the bandwidth efficient multiple access (BEMA) approach (Varanasi, M.K. and Guess, T., IEEE Trans. Commun., vol.49,no.5, p.844-54, 2001) is considered, wherein signals are designed at the base station and fed back to, and for use by, uplink transmitters, in order to minimize a strict bandwidth while ensuring that each user meets a rate-specified QoS constraint. A new recursive, greedy algorithm for signal design is proposed that exactly meets the QoS requirements. Preliminary analysis and numerical examples suggest it is optimal. View full abstract»

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  • An authentication scheme based on roots of sparse polynomials

    Page(s): 159 - 162
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB) |  | HTML iconHTML  

    We describe an authentication scheme whose security is based on the hardness of finding roots of systems of sparse polynomial equations in many variables and of high degree. One of the new ideas is the use of many keys. In one authentication session, a small amount of information about only one of them, chosen randomly, is released; this may be useful in other situations as well. Although the practicality of this scheme has still to be investigated, we believe that the new ideas described here may be of independent interest. View full abstract»

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  • Signature coding over multiple access OR channel

    Page(s): 115 - 118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (397 KB) |  | HTML iconHTML  

    The problem of signature coding for a multiple access OR channel is studied. For the binomial model of the activity of the users, the Kautz-Singleton code and a random code are compared. The minimal code length of the random code is proved to be better than the existing bounds. View full abstract»

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  • Behavior of outage probability in MISO systems with no channel state information at the transmitter

    Page(s): 353 - 356
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (451 KB) |  | HTML iconHTML  

    It is well known that, in terms of the ergodic capacity, the optimum transmit strategy is to allocate equal power to all available transmit antennas. We show that this transmit strategy is not the optimal one for minimizing the outage probability. The optimum strategy is then to avoid using all available antennas. The optimal number of active antennas depends on the required rate and the SNR. We propose an algorithm which computes the optimum number of active antennas for a given available number of transmit antennas, SNR, and rate. We compare the optimum strategy to equal power allocation. View full abstract»

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  • Analysis of mapping strategies for turbo-coded space-time block codes

    Page(s): 103 - 106
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB) |  | HTML iconHTML  

    We propose a "turbo" coding scheme for the multiple-input multiple-output (MIMO) Rayleigh fading channel consisting of the serial concatenation of a block code as the outer code and different orthogonal space-time block codes (STBC) for more than two transmit antennas as the inner code. Here, we consider the orthogonal STBC as a mapping scheme in space and time. At the receiver, we apply iterative space-time detection and decoding. We analyze the impact of different mapping strategies on the information transfer of the soft-input-soft-output (SISO) space-time detector. Moreover, we analytically show that additional performance gains over Gray mapping can be obtained by different mapping strategies. Furthermore, we use extrinsic information transfer characteristics (EXIT-charts) in order to predict the performance and the behavior of the system. View full abstract»

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  • Fast decoding algorithm for LDPC over GF(2q)

    Page(s): 70 - 73
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (457 KB) |  | HTML iconHTML  

    We present a modification of belief propagation that enables us to decode LDPC codes defined on high order Galois fields with a complexity that scales as p log2 (p), p being the field order. With this low complexity algorithm, we are able to decode GF(2q) LDPC codes up to a field order value of 256. We show by simulation that ultra-sparse regular LDPC codes in GF(64) and GF(256) exhibit very good performance. View full abstract»

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  • Performance analysis of MAP decoded space-time orthogonal block codes for non-uniform sources

    Page(s): 46 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (444 KB) |  | HTML iconHTML  

    We derive a closed-form expression for the exact pairwise error probability (PEP) of a non-uniform memoryless binary source transmitted over a Rayleigh fading channel using space-time orthogonal block codes and maximum a posteriori (MAP) detection. The expression is easy to evaluate and holds for any signaling scheme. We then use this result to minimize the bit error rate of the binary antipodal signaling scheme. Numerical results for the case of binary antipodal signaling (BPSK and optimal) verify the accuracy of our formula and quantify substantial gains of MAP decoding over maximum likelihood (ML) decoding for sources with strong non-uniformity. View full abstract»

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  • Spherical designs in four dimensions

    Page(s): 253 - 258
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    A preliminary report on our investigations into the existence of spherical t-designs on the unit sphere Ω4 in 4-dimensional Euclidean space. Tables are given of the putatively best t-designs with up to 100 points. Some general constructions are proposed and explicit constructions are given for N-point strength t designs with N=4p and t=min{p-1,5}, N=6p and t=min{p-1,7}, and N=12p and t=min{p-1,11}, for all p ≥ 1. View full abstract»

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  • Study of bit-interleaved coded space-time modulation with different labeling

    Page(s): 199 - 202
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (501 KB) |  | HTML iconHTML  

    A bit-interleaved concatenated coding scheme consisting of an outer convolutional code and an inner space-time modulation together with an iterative decoding-demapping method is analyzed. As a result, two parameters based on bitwise pairwise error probabilities (b-PEP) for the cases with and without a-priori knowledge are proposed as new measures for a labeling of signal points suited to iterative decoding-demapping. In particular, we demonstrate that the two parameters are closely related to the transfer characteristic (TC) of the demapper and accordingly lead to the same design guideline as a TC analysis. By optimizing these two analytical parameters for an orthogonal space-time block code (oSTBC) employing 16QAM constituent symbols w.r.t. an outer simple 4-states rate 1/2 convolutional code, a highly power efficient concatenated scheme with rate of 2 bits per channel use is proposed, which offers an excellent trade off between power efficiency and complexity. View full abstract»

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  • Generalized minimum distance iterative decoding of expander codes

    Page(s): 245 - 248
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (449 KB) |  | HTML iconHTML  

    Recently, G. Zemor (see IEEE Trans. Inf. Theory, vol.47, p.835-7, 2001) proposed an improvement on the Sipser-Spielman analysis of expander codes (Sipser, M. and Spielman, D.A., IEEE Trans. Inf. Theory, vol.42 , p.1710-22, 1996) and presented a linear-time iterative decoder that can correct a number of errors up to approximately 1/4 the known lower bound on the minimum distance of the code. We propose an improvement on Zemor's decoder for F=GF(2), with the number of correctable errors becoming close to half the lower bound on the minimum distance. The improvement is obtained by inserting into the decoding algorithm features akin to generalized minimum distance decoding of concatenated codes. View full abstract»

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  • A complexity reducing transformation in algebraic list decoding of Reed-Solomon codes

    Page(s): 10 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (505 KB) |  | HTML iconHTML  

    The main computational steps in algebraic soft decoding, as well as Sudan-type list decoding, of Reed-Solomon codes are interpolation and factorization. A series of transformations is given for the interpolation problem that arises in these decoding algorithms. These transformations reduce the space and time complexity to a small fraction of the complexity of the original interpolation problem. A factorization procedure that applies directly to the reduced interpolation problem is also presented. View full abstract»

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  • On the diversity-vs-rate tradeoff in MIMO systems

    Page(s): 357 - 360
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (498 KB) |  | HTML iconHTML  

    Diversity-vs-rate tradeoffs of linear space-time constellations are investigated under different constraints on the peak power, receiver complexity, and rate scaling with the signal-to-noise ratio (multiplexing gain). New constellations from the threaded algebraic space-time (TAST) signaling framework are shown to achieve the optimal tradeoffs. View full abstract»

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  • Partial Reed Solomon codes for erasure channels

    Page(s): 82 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (507 KB) |  | HTML iconHTML  

    We introduce a new family of linear block codes, which we refer to as partial Reed Solomon (PRS) codes. These codes are specifically designed and optimized for real-time multimedia communication over packet-based erasure channels. Based on the constraints and flexibilities of real-time applications, we define a performance measure, message throughput (τm), which is suitable for these applications. This measure differentiates the notion of optimum codes for the target multimedia applications as compared to performance measures that are used for nonreal-time data. Based on the proposed measure, we combine the advantages of lowering the density of a code for near capacity performance with the high decoding efficiency of Reed Solomon (RS) codes, in order to design optimum PRS codes. Then, we demonstrate, through an example of a binary erasure channel (BEC), that at near-capacity coding rates, the appropriate design of a PRS code can outperform an RS-code. We extend this analysis and optimization for a general BEC over a wide range of channel conditions. Moreover, as compared with RS codes, the proposed PRS codes provide a significantly improved graceful degradation when the number of losses exceeds the number of parity symbols within the code block. This is a highly desirable feature for real-time multimedia applications. View full abstract»

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  • A Reed-Solomon decoding algorithm for correcting bursts of erasures in real-time data in packet switched networks

    Page(s): 58 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB) |  | HTML iconHTML  

    In some networks, data packets either arrive without any bit errors, or one or more packets are lost, with packet switched networks as one of the most evident examples. With real-time data, the delay introduced while recovering from these losses can have a great influence on the quality of service of the application. The paper introduces a decoding algorithm that can recover from bursts of erasures by utilizing cyclic Reed-Solomon codes. View full abstract»

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  • Robust slope region for wideband CDMA with multiple antennas

    Page(s): 26 - 29
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (442 KB) |  | HTML iconHTML  

    We analyze a low power, wideband CDMA system with multiple antennas. The joint "slope region" - of transmission rates at minimum energy per bit s derived as a function of proportion between vanishing rates for multiple users. Vertices of the slope region may be achieved by a matched filter linear interface, followed by successive interference cancellation. We introduce and evaluate the "robust slope region", the largest region which is inside every other slope region and is therefore independent of the relative proportion between transmission rates. Furthermore, we find the "robust slope", the maximum slope which can always be guaranteed to all users. View full abstract»

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  • On the symmetric information rate of two-dimensional finite state ISI channels

    Page(s): 320 - 323
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB) |  | HTML iconHTML  

    We derive upper and lower bounds on the symmetric information rate of a two-dimensional finite-state intersymbol-interference (ISI) channel model. View full abstract»

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