Orthogonal transmultiplexers in communication: a review

This paper presents conventional and emerging applications of orthogonal synthesis/analysis transform configurations (transmultiplexer) in communications. It emphasizes that orthogonality is the underlying concept in the design of many communication systems. It is shown that orthogonal filter banks (subband transforms) with proper time-frequency features can play a more important role in the design of new systems. The general concepts of filter bank theory are tied together with the application-specific requirements of several different communication systems. Therefore, this paper is an attempt to increase the visibility of emerging communication applications of orthogonal filter banks and to generate more research activity in the signal processing community on these topics     

Unbiased blind adaptive channel identification and equalization

The blind adaptive equalization and identification of communication channels is a problem of important current theoretical and practical concerns. Previously proposed solutions for this problem exploit the diversity induced by sensor arrays or time oversampling, leading to the so-called second-order algebraic/statistical techniques. The prediction error method is one of them, perhaps the most appealing in practice, due to its inherent robustness to ill-defined channel lengths as well as for its simple adaptive implementation. Unfortunately, the performance of prediction error methods is known to be severely limited in noisy environments, which calls for the development of noise (bias) removal techniques. We present a low-cost algorithm that solves this problem and allows the adaptive estimation of unbiased linear predictors in additive noise with arbitrary autocorrelation. This algorithm does not require the knowledge of the noise variance and relies on a new constrained prediction cost function. The technique can be applied in other noisy prediction problems. Global convergence is established analytically. The performance of the denoising technique is evaluated over GSM test channels     

Audio watermarking under desynchronization and additive noise attacks

Digital watermarking is often modeled as the transmission of a message over a noisy channel denoted as "watermark channel". Distortions introduced by the watermark channel result mainly from attacks and may include interference from the original signal. One of the main differences with classical transmission situations stems from the fact that perceived distortions have to be taken into account. However, measuring the perceived impact an attack has on a watermarked signal is currently an unsolved problem. Possible means of circumventing this problem would be 1) to define the distortion in a so-called "perceived domain" and define an "ad hoc" equivalence between objective and perceived distortion or 2) to define an "equivalent distortion" by removing from the attack noise the part that is correlated to the host signal. This paper concentrates on the second approach and first shows that the resulting "equivalent" attack is a particular case of a thoroughly studied channel: filtering plus additive noise. However, the approach in this paper emphasizes the fact that the additive noise in the model has to be decorrelated with the signal. Then, the formalism is applied to (desynchronization plus noise) attacks on audio signals. In this context, this paper provides the corresponding capacities, as well as optimal "attack" and "defense" strategies in a game theory context.     

Blind identification of multipath channels: a parametric subspaceapproach

In this paper, blind identification of single-input multiple-output (SIMO) systems using second-order statistics (SOS) only is considered. Using the assumption of a specular multipath channel, we investigate a parametric variant of the so-called subspace method. Nonparametric subspace-based methods require precise estimation of the model order; overestimation of the model order leads to inconsistent channel estimates. We show that the parametric subspace method gives consistent channel estimates when only an upper bound of the channel order is known. A new algorithm, which exploits parametric information on the channel structure, is presented. A statistical performance analysis of the proposed parametric subspace criterion is presented; limited Monte Carlo experiments show that the proposed algorithm is second-order optimal for a large class of channels     

Recent developments in the core of digital signal processing

In this article members of the Digital Signal Processing (DSP) Technical Committee (TC) report recent breakthroughs in signal processing fundamentals that have happened in the last two decades. These breakthroughs include various advances and extensions from old techniques to new techniques. For example, signal processing techniques have moved from single-rate to multirate processing, from time-invariant to adaptive processing, from frequency-domain (the traditional Fourier transform, as we know it) to time-frequency analysis, and from linear to non-linear signal processing. Recent developments in these areas have not only renovated the theory of digital signal processing, they have also resulted in new tools that find applications in various domains. For instance, multirate signal processing has triggered recent advances in modem technology and speech/audio coding; adaptive filtering has made echo cancellation and noise suppression possible; time-frequency analysis has found its way into various applications in radar and medical signal processing; and non-linear processing has made engineers rethink various problems in speech recognition and image analysis. This article provides an extensive list of highlights from these recent developments.     

Comparison of electrical and atomic profiles of Mg24 and Zn64 implanted gaas samples and GaAs-GaAIAs heterostructures for bipolar transistor applications

The aim of this work is to study the electrical properties of Mg²⁴ and Zn⁶⁴ implanted and annealed samples (semi-insulating GaAs substrates,n ⁺ doped GaAs epilayers, GaAs-GaAlAs heterostructures) with the final objective of realizing the contact region for the p-type base layer of heterojunction bipolar transistor (HBT). We show that, for HBT applications, Mg⁺ is a more suitable candidate because its characteristics (depth, concentration) are easier to control: they are not very sensitive to doping level and composition of different layers. Low specific contact resistivity (<10^-5Ωcm²) have been obtained with Au-Mn alloy on Mg⁺ implanted GaAs.     

Intergranular Oxidation of Nickel-Base Alloys: Potentialities of Focused Ion Beam Tomography

Oxidation of Metals - The present work focuses on the intergranular oxidation of Alloy 600 and its weld material Alloy 82 after exposure in simulated primary water at 340–360&nbsp;°C...