1,721,058 research outputs found
Basis expansion adaptive filters for time-varying system identification
No full textElectrical Engineering, Mathematics and Computer Scienc
Reduced-Complexity Equalization for MC-CDMA Systems over Time-Varying Channels
No full textWe present a low-complexity equalizer for multicarrier code-division multiple-access (MC-CDMA) downlink systems over time-varying (TV) multipath channels with non-negligible Doppler spread. The equalization algorithm, which is based on a block minimum mean-squared error (MMSE) approach, exploits the band structure of the frequency-domain channel matrix by means of a band LDLH factorization. The complexity of the proposed block MMSE equalizer is linear in the number of subcarriers, and smaller with respect to a serial MMSE equalizer characterized by a similar performance
Block DFE and Windowing for Doppler-Affected OFDM Systems
No full textRecently, a minimum mean-squared error (MMSE) block linear equalizer based on a band LDLH factorization has been proposed for equalization of orthogonal frequency-division multiplexing (OFDM) systems affected by Doppler spread. In this paper, we extend this approach towards two directions. First, we design an MMSE block decision-feedback equalizer (DFE) based on the band LDLH factorization. Both performance and complexity are analyzed. Second, we enhance the performance of the linear equalizer by means of receiver windows tailored to the band LDLH factorization approach. Simulation results show that the proposed techniques are effective in reducing the error floor caused by the intercarrier interference (ICI)
Low-complexity frequency-domain turbo equalization for single-carrier transmissions over doubly-selective channels
No full textSingle-carrier transmissions with frequency-domain equalization have gained much interest due to their comparable complexity and performance to OFDM, which conversely suffers from a high peak-to-average power ratio. In this paper, we develop a new frequency-domain block turbo equalizer for single-carrier (SC) transmissions over doubly-selective channels. The main feature of the proposed equalizer is its low complexity, which is only linear in the block length. A comparison between SC and OFDM systems with channel coding in doubly-selective channels is also given
Iterative channel estimation and turbo equalization for time-varying OFDM systems
No full textWe develop a new receiver for orthogonal frequency division multiplexing (OFDM) systems in time-varying channels by embedding channel estimation in a low-complexity block turbo equalizer. A linear minimum mean squared error (MMSE) pilot-assisted channel estimator is presented, and the soft data estimates from the turbo equalizer are used to improve the quality of the channel estimates
Adaptive Channel Estimation for OFDM Systems with Doppler spread
No full textIn this paper, we propose adaptive channel estimation for orthogonal frequency division multiplexing (OFDM) in fast time-varying (TV) channels. A basis expansion model (BEM) approach is used to capture the time variation of the channel within each OFDM block, and to reduce the estimator dimensionality. Capitalizing on the BEM structure and on a frequency domain training, two adaptive approaches are proposed, based on Kalman filtering and recursive least squares (LS) methods, which exploit the time correlation of the channel between successive blocks and do not require any a-priori knowledge of the channel statistics. Simulation results show that, compared to classical least squares and statistically-aided linear minimum mean squared error (LMMSE) approaches, the two proposed techniques effectively estimate the channel, adapt fast to its non stationary changes, thus enabling efficient TV channel equalization of the inter-carrier interference (ICI) induced in OFDM systems by high Doppler spreads
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
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