Spectral Efficient Coding Schemes in Optical Communications

Abstract Achieving high spectral efficiency in optical transmissions has recently attracted much attention, aiming to satisfy the ever increasing demand for high data rates in optical fiber co mmun ications. Therefore, strong Forward Error Correct ion (FEC) coding in co mb ination with mult ilevel modulat ion schemes is mandatory to approach the channel capacity of the transmission link. In this paper we g ive design rules on the joint optimization of coding and signal constellations under practical considerations. We give trade-offs between spectral efficiency and hardware complexity, by comparing coding schemes using capacity achieving constellations with bit-interleaved coded modulation and iterative decoding (BICM-ID) against applying conventional square quadrature amp litude modulation (QAM) constellations but emp loying powerful low co mplexity lo w-density parity-check (LDPC) codes. Both schemes are suitable for optical single carrier (SC) and optical orthogonal frequency-division mu ltiplexing (OFDM) transmission systems, where we consider the latter one in this paper, due to well-studied equalizat ion techniques in wireless communications. We numerically study the performance of different coded modulation formats in optical OFDM transmission, showing that for a fiber optical transmission lin k of 960 km reach the net spectral efficiency can be increased by ≈0.4 bit/s/Hz to 8.61 b it/s/Hz at a post FEC BER of <10 -15 by using coded optimized constellations instead of coded 64-QAM

A relation between algebraic and transform-based reconstruction technique in computed tomography

In this contribution a coherent relation between the algebraic and the transform-based reconstruction technique for computed tomography is introduced using the mathematical means of two-dimensional signal processing. There are two advantages arising from that approach. First, the algebraic reconstruction technique can now be used efficiently regarding memory usage without considerations concerning the handling of large sparse matrices. Second, the relation grants a more intuitive understanding as to the convergence characteristics of the iterative method. Besides the gain in theoretical insight these advantages offer new possibilities for application-specific fine tuning of reconstruction techniques

Automatic focus algorithms for TDI X-Ray image reconstruction

In food industry, most products are checked by X-rays for contaminations. These X-ray machines continuously scan the product passing through. To minimize the required X-ray power, a Time, Delay and Integration (TDI) CCD-sensor is used to capture the image. While the product moves across the sensor area, the X-ray angle changes during the pass. As a countermeasure, adjusting the sensor shift speed on a single focal plane of the product can be selected. However, the changing angle result in a blurred image in dependance to the thickness of the product. This so-called ''laminographic effect'' can be compensated individually for one plane by inverse filtering. As the plane of contamination is unknown, the blurred image will be inversely filtered for different planes, but only one of these images shows the correctly focussed object. If the correct image can be found, the plane containing the contamination is identified. In this contribution we demonstrate how the correctly focussed images can be found by analyzing the images of all planes. Different characteristics for correctly and incorrectly focussed planes like sharpness, number of objects and edges are investigated by using image processing algorithms

Immobilization, Trapping, and Anion Exchange of Perrhenate Ion Using Copper-Based Tripodal Complexes

We describe a multidentate tripodal ligand in which three pendant arms carrying di(2-picolyl)amine units are linked to the ortho positions of a tris(o-xylyl) scaffold, providing N(CH[subscript 2]-o-C[subscript 6]H[subscript 4]CH[subscript 2]N(CH2py)[subscript 2])[subscript 3] (L). Reaction of L with CuCl[subscript 2] in the presence of hexafluorophosphate anion afforded blue cubes of [(CuCl)[subscript 3]L](PF[subscript 6])[subscript 3]·5H[subscript 2]O (1). Crystallographic studies of 1 revealed that the three symmetry-related arms each coordinate a {Cu[superscript II]Cl} unit, and two molecules of 1 are connected to one another through a Cu(μ-Cl)[subscript 2]Cu bridge, extending the molecular structure to form a two-dimensional (2-D) layer. These 2-D layers pack in an ABCABC... fashion with PF[subscript 6]– anions located in between. Reaction of 1 with a stoichiometric amount of perrhenate ion afforded blue plates of [(CuCl)[subscript 3]L](PF[subscript 6])(ReO[subscript 4])[subscript 2]·3H[subscript 2]O (2). Compound 2 has the same lattice structure as 1, but the tricopper unit backbone now traps one ReO[subscript 4]– anion through Coulombic interactions. In addition, three molecules of 2 are bridged by a perrhenate ion, forming a Cu[subscript 3](μ[superscript 3]-ReO[subscript 4]) cluster, to give a different 2-D structure displaying a rare tridentate bridging ReO[subscript 4]– mode. Thus, in addition to classic perrhenate trapping through weak Coulombic interactions, 2 represents an exceptional example in which the ReO[subscript 4]– anion is immobilized in an extended framework through tight covalent interactions. The interlamellar PF[subscript 6]– anions in 1 can be exchanged with other anions including perrhenate, perchlorate, or periodate. The structural similarity between perrhenate and pertechnetate makes these materials of potential interest for pertechnetate trapping

(Per)chlorate reduction by an acetogenic bacterium, Sporomusa sp., isolated from an underground gas storage

A mesophilic bacterium, strain An4, was isolated from an underground gas storage reservoir with methanol as substrate and perchlorate as electron acceptor. Cells were Gram-negative, spore-forming, straight to curved rods, 0.5–0.8 μm in diameter, and 2–8 μm in length, growing as single cells or in pairs. The cells grew optimally at 37°C, and the pH optimum was around 7. Strain An4 converted various alcohols, organic acids, fructose, acetoin, and H2/CO2 to acetate, usually as the only product. Succinate was decarboxylated to propionate. The isolate was able to respire with (per)chlorate, nitrate, and CO2. The G+C content of the DNA was 42.6 mol%. Based on the 16S rRNA gene sequence analysis, strain An4 was most closely related to Sporomusa ovata (98% similarity). The bacterium reduced perchlorate and chlorate completely to chloride. Key enzymes, perchlorate reductase and chlorite dismutase, were detected in cell-free extracts

Consolidating Heterogeneous Enterprise Data for Named Entity Linking and Web Intelligence

Linking named entities to structured knowledge sources paves the way for state-of-the-art Web intelligence applications which assign sentiment to the correct entities, identify trends, and reveal relations between organizations, persons and products. For this purpose this paper introduces Recognyze, a named entity linking component that uses background knowledge obtained from linked data repositories, and outlines the process of transforming heterogeneous data silos within an organization into a linked enterprise data repository which draws upon popular linked open data vocabularies to foster interoperability with public data sets. The presented examples use comprehensive real-world data sets from Orell Füssli Business Information, Switzerland's largest business information provider. The linked data repository created from these data sets comprises more than nine million triples on companies, the companies' contact information, key people, products and brands. We identify the major challenges of tapping into such sources for named entity linking, and describe required data pre-processing techniques to use and integrate such data sets, with a special focus on disambiguation and ranking algorithms. Finally, we conduct a comprehensive evaluation based on business news from the New Journal of Zurich and AWP Financial News to illustrate how these techniques improve the performance of the Recognyze named entity linking component

Filterverfahren zur Stoerunterdrueckung fuer den Empfang spektral gespreizter Sendesignale

TIB Hannover: DR 7564 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman