1,720,979 research outputs found
On the peak-to-average power ratio of pre-equalized multi-carrier code-division multiple-access transmissions
No full textRecently, pre-equalization for multi-carrier code-division multiple-access (MC-CDMA) systems has attained increased interest. In addition, combined-equalization has been proposed to further enhance the error rate performance of conventional MC-CDMA systems. However, an important issue, peak-to-average power ratio (PAPR), has not been addressed within such systems in the literature. The purpose of this paper is to fill this gap. In particular, we focus on uplink MC-CD MA with pre- or combined-equalization and analyze its PAPR. A general expression for the PAPR of uplink MC-CDMA is derived and some analytical properties are provided. It turns out that PAPR significantly depends on applied pre-equalization technique. Thus, we show how pre-equalization coefficients could be designed in order to reduce PAPR
OFDM synchronization in an uncoordinated spectrum sharing scenario
No full textIn this paper synchronization of uncoordinated OFDM spectrum sharing systems that operate in the presence of narrowband interference (NBI) is analyzed. Conventional synchronization algorithms based on correlation of synchronization preamble in time domain suffer from considerable performance degradation when NBI is present. To overcome this degradation we propose and analyze a method to detect NBI presence and to suppress its influence on synchronization before estimation of synchronization parameters is performed at the OFDM receiver. We focus on an OFDM WLAN system operating in license-exempt band and analyze synchronization performance when NBI is active. The proposed method does not introduce any additional preamble overhead with respect to existing WLAN preamble and requires only slightly higher computational complexity at the receiver. To illustrate effectiveness of the proposed method, several numerical examples are provided
RECEIVER APPARATUS FOR DETECTING NARROWBAND INTERFERENCE IN A MULTI-CARRIER RECEIVE SIGNAL
No full textReceiver apparatus, transmitter apparatus and communication system for detecting a narrowband interference in a multi-carrier receiver signal
No full textMMSE Pre-Filtering techniques for Downlink MC-CDMA transmissions
No full textWe discuss signal pre-filtering in the downlink of a multi-carrier code-division-multiple-access (MC-CDMA) network operating in a time-division-duplex (TDD) mode. The base station (BS) is equipped with multiple antennas and channel state information (CSI) is available at the transmit side due to the channel reciprocity between uplink and downlink transmissions. The pre-filtering coefficients are designed so as to minimize the sum of mean square errors at all mobile terminals (MTs). The resulting scheme mitigates the detrimental effects of multiple access interference (MAI) and multipath propagation, thereby allowing the use of simple and power efficient single-user detection (SUD) techniques at the MTs. Simulation results are given to highlight the effectiveness of the proposed method with respect to other existing pre-filtering schemes
On the Performance of Cancellation Carrier-Based Schemes for Sidelobe Suppression in OFDM Networks
No full textAn efficient scheme for limiting the inherent high out-of-band radiation of the orthogonal frequency-division multiplexing signal has been studied by Brandes el al.. The scheme achieves sidelobe suppression by using few subcarriers, referred to as cancellation carriers (CCs), positioned at the edges of the spectrum and modulated by data-dependent complex-valued symbols that are designed so as to minimize the out-of-band radiation. Unfortunately, its performance has been investigated at the input of the power amplifier (PA) without considering the spectral re-growth induced by PA's non-linear region. Motivated by the above consideration, in this work we return to the aforementioned scheme and investigate its performance at the output of the PA. In addition, since reducing the time-domain signal peaks may alleviate the problem of spectral re-growth, we also adopt two well-known tone reservation (TR)-based peak reduction algorithms
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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