1,721,309 research outputs found
Trace orthogonal space-time coding for multiuser systems
No full textIn this paper we prove that trace-orthogonal space-time coding provides a necessary and sufficient condition for information loss-less coding in a multiple access system, where each user encodes its own symbols independently of the other users. Then, we show that the sub-optimal MMSE decoder can be implemented very simply as a set of scalar decoders and we prove that, under the assumption of using the (sub-optimal) MMSE decoder, the traceorthogonal design with scaled unitary coding matrices yields minimum BER for each user. © 2005 IEEE
Iterative MMSE Decoder for Trace-Orthogonal Space-Time Coding
No full textTrace-orthogonality is an important property of linear space-time encoders that has emerged relatively recently. In this work we carry out the theoretical performance analysis of a low complexity decoder for Trace-Orthogonal space-time codes based on the linear MMSE estimator. We derive the diversity order of such a decoder in the case of MIMO systems affected by uncorrelated flat Rayleigh fading, when information symbols are carved from a QPSK constellation, and are encoded using what we term a Unitary Trace-Orthogonal Design. Then we propose an iterative decoder that dramatically improves the performance over the linear MMSE decoder. Simulation results give evidence of the effectiveness of the proposed scheme. © 2006 IEEE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A novel tunable-complexity turbo-soft detector for high-throughput HDSL applications over ISI channels with crosstalk
No full textIn this paper, we present a novel iterative (turbo) receiver with tunable complexity for reliable detection of (uncoded) payload data transmitted over long intersymbol interference (ISI) channels affected by crosstalk, as those typically encountered in emerging HDSL2 services standardized by ANSI T1.418 recommendation. The proposed receiver combines in an original way "minimum mean square error (MMSE) estimation principle," "turbo-processing principle" and "crosstalk-prediction principle" for achieving both suboptimal maximum a posteriori probability channel equalization and reliable soft-mitigation of ISI tail plus crosstalk. More in detail, according to the turbo-processing principle, at each iteration suitable extrinsic informations are extracted from the equalizing and interference-canceling modules and are used as "a priori information" for the next iteration. Several simulation results on typical HDSL-like test-loops confirm superiority of the proposed turbo-detector (TD) over current solutions based on conventional MMSE decision-feedback equalizers and precoders (such as the Tomlinson-Harashima precoder). The numerical tests also point out that performance of the presented TD on typical high bit-rate digital subscriber lines (HDSLs) is not limited by error-floor phenomena, even at error-probabilities below 10(-7)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Novel efficient bit-loading algorithms for peak-energy-limited ADSL-type multicarrier systems
No full textIn this paper, we develop solutions for the loading of digital subscriber loop (DSL) multicarrier (MC) systems that present constraints both on overall available energy and maximum energy per carrier. In the emerging G.DMT-based systems planned for high-throughput multimedia applications, the constraint on the peak-energy arises from spectral compatibility issues. However, until today, optimal solutions for loading peak-energy constrained MC systems do not seem explicitly developed in the literature. Hence, starting from suitable applications of the Kuhn-Tucker conditions, in this paper, we present the analytical relationships characterizing the optimal solution of the peak-energy-limited loading for the general case of concave "rate-functions," and then, we apply them in the context of the so-called "gap analysis." Thus, a low-complexity iterative algorithm implementing this solution is also developed, and its performance is numerically tested on several ANSI-standard asymmetric DSL (ADSL)-type loops impaired by crosstalk. Furthermore, a version of the presented loading algorithm that guarantees integer bit rates with low computational effort is also presented, and its performance is tested. The carried-out performance comparisons allow us to evaluate the throughput loss induced by peak-energy constraints in emerging ADSL-like services
Information Lossless Space-Time Coding for Multiple Access Systems
No full textIn this paper we consider multiple access systems where users and access point are equipped with multiple antennas. In order to exploit some of the MIMO potentials we have to resort to space-time coding. Unfortunately, such a processing may induce severe loss in terms of achievable information rates. In this paper we prove the necessary and sufficient condition ensuring that the space-time coding is information lossless, in the sense that it does not induce any modification in certain regions of achievable rates. In particular information lossless property is guaranteed if each user makes use of a Trace-Orthogonal Design (TOD), that is a linear space-time code whose encoding matrices are orthogonal with respeet to the trace inner product. Noteworthy, users can also use the same set of encoding matrices. © 2007 IEEE
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