1,721,197 research outputs found
Multi-Stage Multi-User Detection Assisted Asynchronous Fast-FH/MFSK
Full text linkA multi-stage Multi-User Detection (MUD) scheme designed for asynchronous fast Frequency-Hopping/Multilevel Frequency-Shift-Keying (fast-FH/MFSK) systems is proposed, in which each signal detection interval is divided into sub-intervals and the MUD is applied to each sub-interval. In our scheme the MUD exploits the explicit knowledge of the hopping addresses assigned to users. The received signal level is attenuated by a constant scaling factor, when it is deemed to be overwhelmed by multi-user interference. For the sake of preventing erroneous detection events, when communicating over frequency-selective fading channels, the scheme advocated also invokes a space diversity technique. In the investigated scenario the achievable Bit Error Rate (BER) of the proposed scheme was reduced by as much as an order of magnitude in comparison to that of a conventional MUD scheme, when transmitting over an AWGN channel. For transmission over a channel exhibiting uncorrelated frequency-domain fading, selection diversity was used for the sake of achieving a reduced BER
Time-Frequency Spread OFDM/FHMA
No full textA combined scheme based on Orthogonal Frequency-Division Multiplexing and Frequency-Hopped Multiple Access (OFDM/FHMA) is proposed, in which the transmitted data is spread over both the time and frequency axes without expanding the bandwidth. The OFDM system advocated employs the Walsh-Hadamard Transform (WHT) for spreading the data in the frequency domain and weights the received signal by the estimated Signal-to-Interference Ratio (SIR) for the sake of reducing the effects of interference. The performance recorded, when communicating over an interference-limited channel suggests that the achievable BER improvement is as much as an order of magnitude in comparison to that of an OFDM/FHMA scheme dispensing with WHT
On the performance of Multi-Stage Multi-User Detection Assisted Fast-FH/MFSK
No full textA multi-stage Multi-User Detection (MUD) scheme designed for a fast Frequency-Hopping/Multilevel Frequency-Shift-Keying (fast-FH/MFSK) system is proposed, which exploits the explicit knowledge of the hopping addresses assigned to users. The received signal level is attenuated by a constant scaling factor, when it is deemed to be overwhelmed by multi-user interference. For the sake of preventing erroneous detection events, when communicating over frequency-selective fading channels, the scheme advocated invokes a variable detection threshold parameter. In the investigated scenario the achievable Bit Error Rate (BER) of the proposed scheme was reduced by as much as an order of magnitude in comparison to that of a Single-User Detection (SUD) scheme when transmitting over an AWGN channel. For transmission over a channel exhibiting uncorrelated frequency-domain fading, a variable – rather than fixed – threshold was used for the sake of achieving reduced BER
Multi-Stage Multi-User Detection Assisted Fast-FH/MFSK
No full textA multi-stage multi-user detection (MUD) scheme designed for a fast-FH/MFSK system is proposed, in which the received signal level is attenuated by a constant scaling factor when the signal is deemed to be overwhelmed by multi-user interference. In the investigated scenario a substantially reduced bit error rate is achieved
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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