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Signal Processing Letters, IEEE

Issue 9 • Date Sept. 2006

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Displaying Results 1 - 21 of 21
  • Table of contents

    Publication Year: 2006 , Page(s): c1 - c4
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  • IEEE Signal Processing Letters publication information

    Publication Year: 2006 , Page(s): c2
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  • From Finite-System Entropy to Entropy Rate for a Hidden Markov Process

    Publication Year: 2006 , Page(s): 517 - 520
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB) |  | HTML iconHTML  

    A recent result presented the expansion for the entropy rate of a hidden Markov process (HMP) as a power series in the noise variable epsi. The coefficients of the expansion around the noiseless (epsi=0) limit were calculated up to 11th order, using a conjecture that relates the entropy rate of an HMP to the entropy of a process of finite length (which is calculated analytically). In this letter, we generalize and prove the conjecture and discuss its theoretical and practical consequences View full abstract»

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  • Implicit MIMO Channel Estimation Without DC-Offset Based on ZCZ Training Sequences

    Publication Year: 2006 , Page(s): 521 - 524
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (163 KB)  

    In this letter, an implicit direct current (dc) free multiple-input multiple-output (MIMO) channel estimation scheme is proposed by employing a set of zero correlation zone (ZCZ) training sequences. The new implicit MIMO channel estimation scheme includes, as a special case, the conventional implicit single-input single-output (SISO) channel estimation scheme, which is also considered and analyzed. For implicit SISO channel estimation, by choosing properly a set of ZCZ sequences with balanced property, the harmful dc-offset can be completely removed, thus exhibiting significantly better estimation performance and resulting in simpler implementation when compared with the conventional implicit training schemes without dc-offset elimination and with dc-offset elimination based on perfect sequences, respectively View full abstract»

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  • A Semidefinite Relaxation Approach to MIMO Detection for High-Order QAM Constellations

    Publication Year: 2006 , Page(s): 525 - 528
    Cited by:  Papers (62)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB) |  | HTML iconHTML  

    A new and conceptually simple semidefinite relaxation approach is proposed for MIMO detection in communication systems employing high-order QAM constellations. The new approach affords improved detection performance compared to existing solutions of comparable worst-case complexity order, which is nearly cubic in the dimension of the transmitted symbol vector and independent of the constellation order for uniform QAM, or affine in the constellation order for nonuniform QAM View full abstract»

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  • Design of Complex FIR Filters With Reduced Group Delay Error Using Semidefinite Programming

    Publication Year: 2006 , Page(s): 529 - 532
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (171 KB) |  | HTML iconHTML  

    This letter proposes an improved method for designing complex finite impulse response (FIR) filters with reduced group delays using semidefinite programming. A key step in the proposed method is to directly impose a group delay constraint, which is formulated as a linear matrix inequality constraint with some reasonable approximations. The main advantage of the proposed design method is the significant reduction in group delay error at the expense of the slight increase in magnitude error. The effectiveness of the proposed design method is illustrated with an example View full abstract»

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  • Orthonormal Hilbert-Pair of Wavelets With (Almost) Maximum Vanishing Moments

    Publication Year: 2006 , Page(s): 533 - 536
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    An orthonormal Hilbert-pair consists of a pair of conjugate-quadrature-filter (CQF) banks such that the equivalent wavelet function of both banks are approximate Hilbert transforms of each other. We found that the celebrated orthonormal wavelets of Daubechies, which have maximum vanishing-moment (VM), cannot be used to construct good Hilbert-pairs. In this letter, we reduce the number of VM by one and construct a Hilbert-pair with almost maximum VM. Each pair of wavelets are time-reverse versions of each other, and the individual wavelets are of the least asymmetric type (i.e., approximate linear phase CQF) View full abstract»

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  • Decomposition of Toeplitz Matrices via Convex Optimization

    Publication Year: 2006 , Page(s): 537 - 540
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (132 KB) |  | HTML iconHTML  

    We point out that autocovariance functions of moving average processes of any given order m can be characterized via a linear matrix inequality (LMI). This LMI-condition can be used to decompose any Toeplitz autococovariance matrix into a sum of a singular Toeplitz covariance plus the autocovariance matrix of a moving average process of order m and of maximal variance. The decomposition is unique and subsumes the Pisarenko harmonic decomposition that corresponds to m=0. It can be used to account for mutual couplings between elements in linear antenna arrays or identify colored noise consistent with the covariance data. The same LMI-condition leads to an efficient computation of the least order of a MA-spectrum that agrees with covariance moments View full abstract»

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  • On the Fourier Transform of Finite Chirps

    Publication Year: 2006 , Page(s): 541 - 544
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (155 KB) |  | HTML iconHTML  

    In this letter, closed-form expressions for the discrete Fourier transform (DFT) of a finite chirp are derived. It is shown that when the normalized chirp rate is coprime with the chirp length, then the DFT of a finite chirp is again a finite chirp with magnitude, chirp rate, and carrier frequency appropriately scaled. In particular, when the normalized chirp rate is of unit value, then the DFT of a finite chirp is the same chirp, up to a complex scaling factor. Conversely, when the normalized chirp rate has a common factor with the chirp length, then the support of the DFT of a finite chirp is equal to the ratio of chirp length and the common factor. Among other things, results given here complement certain results, obtained by Janssen, on the computation of time-continuous chirps with rational sweep rates View full abstract»

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  • On the Fractional Wideband and Narrowband Ambiguity Function in Radar and Sonar

    Publication Year: 2006 , Page(s): 545 - 548
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (171 KB) |  | HTML iconHTML  

    We construct the wideband ambiguity function for signals represented by their fractional Fourier transforms. Because the reflected signal must be represented as a Doppler scaled version of the transmitted signal, this wideband form of ambiguity does not enjoy many of the same properties as the narrowband form (which is formed from a Doppler shifted version of the signal). We present the general result and also examine an approximation appropriate to wideband signals reflected from slowly moving targets View full abstract»

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  • Integral Invariants for Computed Tomography

    Publication Year: 2006 , Page(s): 549 - 552
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (447 KB) |  | HTML iconHTML  

    Using the group theory, we formulate integral invariants of projection data in fan-beam and cone-beam computed tomography (CT), which can be applied to sense an object motion and detect a contrast bolus arrival View full abstract»

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  • Visual Entropy Gain for Wavelet Image Coding

    Publication Year: 2006 , Page(s): 553 - 556
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (878 KB) |  | HTML iconHTML  

    Wavelet image coding exhibits a robust error resilience performance by utilizing a naturally layered bitstream construction over a band-limited channel. In this letter, a new measure that appears to provide a better assessment of visual entropy for comparing and evaluating progressive image coders is defined based on a visual weight over the wavelet domain. This visual weight is characterized by the human visual system (HVS) over the frequency and spatial domains and is then utilized as a criterion for determining the coding order of wavelet coefficients, resulting in improved visual quality. A transmission gain, which is expressed by visual entropy, of up to about 23% can be obtained at a normalized channel throughput of about 0.3. In accordance with the subjective visual quality, a relatively high gain can be obtained at a low channel capacity View full abstract»

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  • cal H_\infty FIR Filters for Linear Continuous-Time State–Space Systems

    Publication Year: 2006 , Page(s): 557 - 560
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (170 KB) |  | HTML iconHTML  

    In this letter, we propose a new Hscrinfin filter (HF) with a finite impulse response (FIR) structure for linear continuous-time state-space systems. This filter is called the Hscr infin FIR filter (HFF). The upper bound for an Hscrinfin performance criterion is derived and then minimized among the filters with linearity, FIR structure, and quasideadbeat property. The HFF is obtained by solving the differential Riccati equation. We show through simulations that the HFF is more robust against temporary uncertainties and is faster in convergence than a conventional HF View full abstract»

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  • Data Adaptive Median Filters for Signal and Image Denoising Using a Generalized SURE Criterion

    Publication Year: 2006 , Page(s): 561 - 564
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    Due to its effectiveness for removing heavy-tail noise and preserving abrupt structures hidden in noisy data, median filtering has long been a popular tool for signal restoration. In practice, an important issue of applying median filtering is the choice of the span. In this letter, we develop a data adaptive criterion for choosing this span. This criterion is derived using the generalized SURE technique recently proposed by Shen and Huang. It is designed to handle outliers and heavy-tail noise, and it aims to minimize the mean-squared error between the true and restored signals. Results from simulation experiments suggest that the proposed criterion is superior to its competitors View full abstract»

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  • Signal Waveform's Optimal-under-Restriction Design for Active Sensing

    Publication Year: 2006 , Page(s): 565 - 568
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    We consider Signal Waveform's Optimal-under-Restriction Design (SWORD) for active sensing. In the presence of colored interference and noise with known statistical properties, waveform optimization for active sensors such as radar can significantly increase the signal-to-interference-plus-noise ratio needed for much improved target detection. However, the so-obtained optimal waveforms can result in significant modulus variation, poor range resolution, and/or high peak sidelobe levels. To mitigate these problems, we can constrain the waveform optimization problem by restricting the sought-after waveform to be similar to a desired waveform, which is known to have, for example, constant modulus as well as reasonable range resolution and peak sidelobe level. One example of the desired waveform is the widely used linear frequency modulated waveform or chirp. We will provide a detailed solution to the constrained optimization problem and explain how it is related with the existing waveform optimization methods View full abstract»

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  • Empirical Lower Bound on the Bitrate for the Transparent Memoryless Coding of Wideband LPC Parameters

    Publication Year: 2006 , Page(s): 569 - 572
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (158 KB) |  | HTML iconHTML  

    In this letter, we determine empirical lower bounds on the bitrate required to transparently code linear predictive coding (LPC) parameters derived from wideband speech. This is achieved via extrapolation of the operating distortion-rate curve of an unconstrained vector quantizer that is trained using artificial vectors generated by a Gaussian mixture model. Memoryless coding is considered and two competing LPC parameter representations are investigated. Our results show a lower bound of 31 bits/frame when assuming high-rate linearity in the operating distortion-rate curve and 35 bits/frame for an exponential curve. We also evaluate a recent quantization scheme and compare its performance against this lower bound View full abstract»

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  • Linear Dynamic Models With Mixture of Experts Architecture for Recognition of Speech Under Additive Noise Conditions

    Publication Year: 2006 , Page(s): 573 - 576
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (159 KB)  

    This letter presents a new approach to enhance speech feature estimation in the log spectral domain under noisy environments. A mixture of linear dynamic models with an architecture similar to the so-called mixture of experts (ME) is investigated to describe the clean speech feature distribution parametrically. Switching Kalman filters are adapted to the proposed model, and they estimate the clean speech components by means of a generalized pseudo-Bayesian (GPB) algorithm. Experimental results suggest that compared with previous methods, the proposed approach can be more powerful to compensate the noisy speech features for robust speech recognition View full abstract»

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  • IEEE Signal Processing Letters Information for authors

    Publication Year: 2006 , Page(s): 577 - 578
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  • Special issue on human detection and recognition

    Publication Year: 2006 , Page(s): 579
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  • Special issue on music information retrieval (MIR)

    Publication Year: 2006 , Page(s): 580
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  • IEEE Signal Processing Society Information

    Publication Year: 2006 , Page(s): c3
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Aims & Scope

The IEEE Signal Processing Letters is a monthly, archival publication designed to provide rapid dissemination of original, cutting-edge ideas and timely, significant contributions in signal, image, speech, language and audio processing.

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Meet Our Editors

Editor-in-Chief
Peter Willett
University of Connecticut
Storrs, CT 06269
peter.willett@uconn.edu