Equal-power coordinated transmission for HDSL

In a two-channel transmission system, the signal-to-noise ratio (SNR) at the receiver can in general be different for the channels. Normally, performance will be dominated by the channel with the worst SNR, but it is possible to do much better. The general scheme proposed provides optimum performance when the SNR varies between the channels and/or when the interference is correlated, without varying the transmitted power for each channel. Simplified schemes attain nearly optimum performance under certain channel conditions     

MMSE decision-feedback equalizers and coding. I. Equalizationresults

The minimum mean-squared-error decision-feedback equalizer (MMSE-DFE) has properties that suggest that it is a canonical equalization structure for systems that combine equalization with coded modulation. The structure and performance of the MMSE-DFE are succinctly derived using linear-estimation-theoretic principles in this first part of this two-part paper. The front-end of the MMSE-DFE, called the “mean-square whitened matched filter” (MS-WMF), is preferable in some ways to a matched filter or a whitened matched filter as a canonical receiver front end. In a coded system, the feedback filter of the MMSE-DFE may be implemented in the transmitter using precoding. The MMSE-DFE can perform significantly better than a zero-forcing decision-feedback equalizer, particularly at moderate-to-low SNR's and on severe-ISI channels. The MMSE-DFE is biased. The optimum unbiased MMSE-DFE is the MMSE-DFE with the bias removed. Removing bias improves error probability, but reduces the SNR to SNR_MMSE-DFE,U=SNR_MMSE-DFE-1. It is shown that this SNR relationship is a particular case of a very general result and that SNR_MMSE-DFE,U gives a more realistic estimate of SNR. The results are extended to partial response equalization and to equalization with correlated inputs in an appendix     

V.92: the last dial-up modem?

Ever since the first dial-up modems appeared in the 1960s, their obsolescence has been repeatedly predicted. However, contrary to such predictions, dial-up modems thrived in the 1980s and 1990s as a result of the slow rollout of residential digital services and the unprecedented growth of internet and remote access. Since the first 300 b/s dial-up modem standard (V.21), modem speeds have increased steadily. Most recently, International Telecommunications Union (ITU) Recommendation V.90 (1998) takes advantage of the direct digital-network connection of an internet service provider (ISP) remote-access server to achieve speeds of more than 50 kb/s downstream (from ISP to a user). However, for upstream transmission (from a user to ISP), V.90 employs the older V.34 modulation (1994), which typically delivers on the order of 30 kb/s. A new ITU modem standard called V.92 increases upstream rates to above 40 kb/s, again by taking advantage of pulse code modulation connections. In this paper, we present the transmission scheme that has been adopted for V.92. It involves a generalization of Tomlinson-Harashima precoding. We predict that V.92 will be the last dial-up modem standard. However, we have to wonder whether we might be falling into the same trap into which many others have fallen in the past. The future will be the judge!.     

Involvement of the Fas/Fas ligand pathway in activation-induced cell death of mycobacteria-reactive human gamma delta T cells: a mechanism for the loss of gamma delta T cells in patients with pulmonary tuberculosis

Although the identity of T cells involved in the protection against Mycobacterium tuberculosis (Mtb) in humans remain unknown, patients with pulmonary tuberculosis (TB) have reduced numbers of Mtb-reactive, V gamma 9+/V delta 2+ T cells in their blood and lungs. Here we have determined whether this gamma deltaT loss is a consequence of Mtb Ag-mediated activation-induced cell death (AICD). Using a DNA polymerase-mediated dUTP nick translation labeling assay, 5% or less of freshly isolated CD4+ alpha beta or gamma delta T cells from normal healthy individuals and TB patients were apoptotic. However, during culture Mtb Ags induced apoptosis in a large proportion of V gamma 9+V delta 2+ peripheral blood T cells from healthy subjects (30-45%) and TB patients (55-68%); this was increased further in the presence of IL-2. By contrast, anti-CD3 did not induce any significant level of apoptosis in gamma delta T cells from healthy subjects or TB patients. Mtb Ag stimulation rapidly induced Fas and Fas ligand (FasL) expression by gamma delta T cells, and in the presence of metalloproteinase-inhibitors >70% of gamma delta T cells were FasL+. Blockade of Fas-FasL interactions reduced the level of Mtb-mediated gamma delta T cell apoptosis by 75 to 80%. Collectively, these findings demonstrate that Mtb-reactive gamma delta T cells are more susceptible to AICD and that the Fas-FasL pathways of apoptosis is involved. AICD of gamma delta T cells, therefore, provides an explanation for the loss of Mtb-reactive T cells during mycobacterial infection.     

Convolutional spectral shaping

A new spectral shaping technique, convolutional spectral shaping (CSS), is introduced. In CSS, equivalence classes of possible sign bit sequences are represented by a coset of a convolutional code and a search through the trellis of the code is used to pick a sequence from the selected coset to approximate a target spectral shape for transmission. Simulation results are included to illustrate the performance of CSS. A version of CSS has been adopted by the International Telecommunication Union (ITU) in the pulse code modulation (PCM) modem standard V.90     

Lattice and trellis quantization with lattice- and trellis-boundedcodebooks-High-rate theory for memoryless sources

High-rate lattice and trellis quantizers for nonuniform sources are introduced and analyzed. The performance of these quantizers is determined by two separable quantities, the granular gain and the boundary gain, which are determined by the shapes of the granular cells and of the support region, respectively. The granular gain and boundary gain are the duals of shaping and coding gain in data transmission applications. Using this duality, it is shown for Gaussian sources that the ultimate achievable boundary gain with high-rate lattice-bounded lattice codebooks is the same as the ultimate gain that can be obtained from variable-rate entropy coding. It is observed that if lattice codebooks can achieve the ultimate granular gain of 0.255 b per dimension, then lattice-bounded lattice codebooks can approach the rate-distortion limit. The performance of lattice quantizers is compared to that of optimum vector quantizers     

The V.34 high speed modem standard

The development of the V.34 modem standard permits full-duplex transmission at rates up to 33.6 kb/s in the ordinary general switched telephone network (GSTN). This article briefly describes the technologies that are used to make these dramatically increased bit rates possible. This new high-speed modem enables various new multimedia modem applications     

Simulated Performance of an Adaptive Multielement Integrated Receiver Structure in Impulse or Burst Noise

We consider the convergence and tracking properties of an adaptive multielement integrated receiver structure operating in the presence of impulsive or burst noise. The receiver structure is integrated in the sense that it incorporates both the spatial/temporal predetection processing and demodulation functions in a single entity. This integrated receiver structure has been developed in previous work to approximate maximum-likelihood (ML) reception in the presence of both intersymbol interference (ISI) and spatially distributed interference (SDI) when the latter is modeled as zero-mean Gaussian noise. The present paper is devoted to a simulation study of the convergence properties of this receiver structure when the SDI is replaced by non-Gaussian impulsive or burst noise. Results indicate that the convergence characteristics are relatively insensitive to the statistics of the SDI provided that secondorder properties are held fixed, at least for moderate deviations from Gaussian behavior. For highly impulsive SDI environments, however, the adaptive system exhibits a complete failure to converge.     

Arc magmatism as a window to plate kinematics and subduction polarity: Example from the eastern Pontides belt, NE Turkey

The Eastern Pontides orogenic belt in the Black Sea region of Turkey offers a critical window to plate kinematics and subduction polarity during the closure of the Paleotethys.Here we provide a brief synthesis on recent information from this belt.We infer a southward subduction for the origin of the Eastern Pontides orogenic belt and its associated late Mesozoic-Cenozoic magmatism based on clear spatial and temporal variations in Late Cretaceous and Cenozoic arc magmatism,together with the existence of a prominent south-dipping reverse fault system along the entire southern coast of the Black Sea.Our model is at variance with some recent proposals favoring a northward subduction polarity,and illustrates the importance of arc magmatism in evaluating the geodynamic milieu associated with convergent margin processes.