1,720,976 research outputs found
An Experimental Approach to CDMA and Interference Mitigation: From System Architecture to Hardware Testing through VLSI Design
No full textThe key of a successful approach to the complex issue of designing wireless terminals for present and future communication systems (usually addressed to as '3rd Generation and beyond') lies in a single 'magic' word: multidisciplinarity. This was actually the philosophy which inspired and drove a fruitful teamwork performed at the University of Pisa (Italy) under the auspices of the European Space Agency (ESA) with the goal of developing a digital receiver for CDMA mobile communications. The most challenging issue of the project was the implementation into a single ASIC device of an advanced detector for multi-user CDMA signals featuring interference mitigation capability. The whole design process, starting from system specifications down to final hardware testing, required quite a demanding and synergic effort, involving telecom engineers on one side and electronic designers on the other. The development and the achievements of the project gave the authors the cue for writing this book whose contents represents the lesson learnt from such an interdisciplinary research activity. An Experimental Approach to CDMA and Interference Mitigation was written with the admittedly ambitious intent of filling the gap between communication theory and VLSI implementation, and thus to provide a more general/theoretical approach to the design, development, and testing of a CDMA receiver. As a consequence, the concepts and techniques that are presented turn out to be applicable to a more general kind of digital wireless modems in terms of receiver architecture design and implementation. As the reader will easily find out, the subject of digital modem design and implementation is addressed in the book starting from a theoretical approach (supported by proper bibliographic references), and is followed by application issues, with reference to an ESA experiment assumed as a case study. A complete design flow, from specification to implementation, including testing and final verification is then presented. This leads the reader step-by-step to a thorough understanding of CDMA transmission and detection, and constitutes a practical guidance for the design of VLSI wireless mobile terminals
Implementation of Message-Passing Algorithms for the Acquisition of Spreading Codes
No full textA new technique to acquire pseudo-noise (PN) sequences has been recently proposed in [1] and [2]. It is based on the paradigm of iterative Message Passing (iMP) to be run on loopy graph. This technique approximates the maximum-likelihood (ML) estimator, providing a sub-optimal algorithm that searches all possible code phases in parallel, at low complexity and fast acquisition time. This work is addressed to the design of the architecture of an iMP detector, following the implementation methodologies typical of standard low-density parity-check (LDPC) decoders, and demonstrates its benefits in terms of acquisition time and complexity, compared with standard techniques
VLSI Design of a High–Throughput Multi–Rate Decoder for Structured LDPC Codes
No full textDespite recent advances in the microelectronics technology, the implementation of high-throughput decoders for LDPC codes remains a challenging task. This paper aims at summarising the top-down design flow of a decoder for a structured LDPC code compliant with the WWiSE proposal for WLAN. Starting from the system performance analysis with finite-precision arithmetic, a high-throughput architecture is presented as an enhancement of the state-of-the-art solutions, and its VLSI design detailed. The envisaged architecture is also very flexible as it supports several code rates with no significant hardware overhead. The overall decoder, synthesised on 0.18 μm standard cells CMOS technology, showed remarkable performances: small implementation loss (0.2 dB down to BER = 10 -8), low latency (less than 6.0 μs), high useful throughput (up to 940Mbps) and low complexity (about 375 Kgates)
A performance analysis of LDPC code decoding under finite-precision arithmetics
No full textWhile several implementations of LDPC codes decoders are available, the effects of fixed-point quantisation are still somewhat obscure. This paper aims at defining a systematic and general methodology to attack the LDPC decoding problem under finite–precision arithmetic. Statistical analysis is completed with Monte Carlo simulations to deploy the basics of the quantisation problem; the key aspect of this work is the independent study of channel reliability and extrinsic messages. As a case example, a short block, structured LDPC code is considered, and the results are shown. The extension to different codes confirms the validity of our method in relating design parameters and performance. This study is at the basis of the exploration of the trade-off between system performance and hardware complexity and can be easily extended to other applications
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
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
- …
