IEEE Signal Processing Letters

A recursive approach for shrinking coefficients of an atomic decomposition is proposed. The corresponding algorithm evolves so as to provide at each iteration 1) the orthogonal projection of a signal onto a reduced subspace and 2) the index of the coefficient to be disregarded in order to construct a coarser approximation minimizing the norm of the residual error. View full abstract»

Iteratively Reweighted Least Squares (IRLS) and Residual Steepest descent (RSD) algorithms of robust statistics arise as special cases of half-quadratic schemes . Here, we adopt a statistical framework and we show that both algorithms are instances of the EM algorithm. The augmented dataset respectively involves a scale and a location mixture of Gaussians. The sufficient conditions for the constru... View full abstract»

In the context of real-time detection of transient signals, a likelihood ratio (LR) test is evaluated at every sampling interval. Performing the LR tests at a lower rate reduces significantly the computational complexity of the detection algorithm. However, in general, this simplification also leads to a strong degradation of the detector performance. For example, with a small shift error, an arri... View full abstract»

We propose a new image denoising algorithm that exploits an image's representation in multiple wavelet domains. Besov balls are convex sets of images whose Besov norms are bounded from above by their radii. Projecting an image onto a Besov ball of proper radius corresponds to a type of wavelet shrinkage for image denoising. By defining Besov balls in multiple wavelet domains and projecting onto th... View full abstract»

We present a new method to study linear systems that exhibit time-varying characteristics and are governed by ordinary differential equations. The method transforms the differential equation into the governing equation for the ambiguity function and to the time-frequency domain. The advantage of the method is that in the new domain an immense simplification occurs, both mathematically and physical... View full abstract»

We propose a noncausal estimator for the a priori signal-to-noise ratio (SNR), and a corresponding noncausal speech enhancement algorithm. In contrast to the decision-directed estimator of Ephraim and Malah (1984), the noncausal estimator is capable of discriminating between speech onsets and noise irregularities. Onsets of speech are better preserved, while a further reduction of musical noise is... View full abstract»

We investigate a new class of training sequences that are optimal for least squares (LS) channel estimation in systems employing transmit diversity and single-carrier (SC) modulation with a cyclic prefix (CP) extension. The sequences have a constant envelope in the time domain and are orthogonal in the frequency domain. Transmission of these sequences facilitates optimal (in the LS sense) estimati... View full abstract»

This work derives a family of dilation matrices for the body-centered cubic (BCC) lattice, which is optimal in the sense of spectral sphere packing. While satisfying the necessary conditions for dilation, these matrices are all cube roots of an integer scalar matrix. This property offers theoretical advantages for construction of wavelet functions in addition to the practical advantages when itera... View full abstract»

We propose a new design criterion for subband adaptive filters (SAFs). The proposed multiple-constraint optimization criterion is based on the principle of minimal disturbance, where the multiple constraints are imposed on the updated subband filter outputs. Compared to the classical fullband least-mean-square (LMS) algorithm, the subband adaptive filtering algorithm derived from the proposed crit... View full abstract»

This letter describes fixed-point implementations of the Winograd and prime factor FFT algorithms in which multiplications are replaced by additions, subtractions and shifts. Methods are described for minimizing the number of additions and subtractions, while achieving a required level of accuracy. VLSI implementation of the resulting FFTs could achieve very high speed and/or power efficiency. The... View full abstract»

Block-based motion estimation is widely used in video compression for exploitation of video temporal redundancy. Although effective, the process is arguably the most computationally intensive part of a typical video encoder. To speed up the process, a large number of fast block-matching algorithms (BMAs) have been proposed for motion estimation by limiting the number of search locations or simplif... View full abstract»

A complex sphere decoding algorithm is presented for signal detection in V-BLAST systems, which has a computational cost that is significantly lower than that of the original complex sphere decoder (SD) for a wide range of SNRs. Simulation results on a 64-QAM system with 23 transmit and 23 receive antennas at an SNR per bit of 24 dB show that the new sphere decoding algorithm obtains the ML soluti... View full abstract»

Three reduced complexity equalization schemes for Zero-padded OFDM systems are described. These schemes guarantee Zero-Forcing (ZF) equalization irrespective of the channel s. Two of these schemes implement the minimum-norm ZF equalizer efficiently using QR decomposition. In the third scheme, the channel zeros are grouped as being inside or outside or on the unit circle. These groups are then equa... View full abstract»

Muquet et al. (2002) have proposed a subspace-based blind method for estimating the channel responses of cyclic-prefixed OFDM systems. Their proof for the channel identifiability uses the roots of channel transfer function and therefore depends on the channel order. When only an upper bound is known for the channel order, the proof fails. In this letter, a new proof for the identifiability is give... View full abstract»

Due to the growing demand for mobile communications, blind adaptive algorithms have an important role in improving data transmission efficiency. In this context, the convergence and tracking analysis of such algorithms is a problem of interest. Recently, a tracking analysis of the Constant Modulus Algorithm was presented based on an energy conservation relation. In this letter we extend that analy... View full abstract»

The low frequency and high amplitude clutter signal constitutes a great disturbance for the discrimination of low velocity blood flow signals in a Doppler ultrasound measurement system. In this letter, a novel method for clutter rejection is proposed, incorporating irregular sampling and iterative reconstruction by cubic spline. Experimental results indicate this approach outperforms the tradition... View full abstract»

Based on a cross-zonal filter in the two-dimensional (2-D) cubic-spline interpolation (CSI) and a symmetric extension method, an efficient algorithm is proposed for image coding. Experimental results show that the proposed method is superior in performance and yields a better quality of reconstructed image than other interpolation methods. View full abstract»

In this letter, an improved square-root algorithm for Bell Labs Layered Space-Time (BLAST) system is proposed. It speeds up the original square-root algorithm by 36% in terms of the number of multiplications and additions. Compared with the recursive algorithm, it requires only a 13.6% higher number of multiplications and a 38.9% higher number of additions. Since it uses unitary transformations to... View full abstract»