1,720,959 research outputs found
Low-Complexity Channel Estimation in OFDM MU-MIMO Next Generation Cellular Networks
No full textWe consider downlink communications between a Base Station (BS) and various mobile stations, equipped with multiple antennas, based on Orthogonal Frequency Division Multiplexing (OFDM). Transmission is compliant with the Long Term Evolution (LTE) standard operating in Frequency Division Duplex (FDD) mode. Since ideal feedback of channel state information to the BS may be cumbersome, we consider two suboptimal channel estimation algorithms, denoted as Resource Block (RB) and Resource Block Group (RBG). Both approaches approximate the channel as constant over multiples of the fundamental LTE block, known as Physical Resource Block (PRB). Our results show that RB and RBG incur a limited performance loss, yet guaranteeing significant saving in the amount of feedback information
Experimental Analysis and Design Guidelines for Microphone Virtualization in Automotive Scenarios
Full text linkIn this article, a performance analysis on the estimation of the so-called observation filter for the Virtual Microphone Technique (VMT) in a realistic automotive environment is presented. A performance comparison between adaptive and fixed observation filter estimation methods, namely Least Mean Square (LMS) and Minimum Mean Square Error (MMSE), respectively, was carried on. Two different experimental setups were implemented on a popular B-segment car. Eight microphones were placed at the monitoring and virtual positions in order to sense environmental acoustic noise propagating within the cabin of the car running at variable speed on a smooth asphalt. Our experimental results show that a large spectral coherence between monitoring and virtual microphone signals indicates a potentially effective and relatively wide-band virtual microphone signal reconstruction. The fixed observation filter estimation method achieves better performance than the adaptive one, guaranteeing remarkable broadband estimation accuracy. Moreover, for each considered setup, design guidelines are proposed to obtain a good trade-off between estimation accuracy and material costs
Heuristic Design of Feedback Active Noise Control for Automotive Applications
No full textIn this paper, a performance analysis of FeedBack (FB) Active Noise Control (ANC) systems for automotive applications is presented. Noise cancellation is obtained from a fixed controller, heuristically designed using concepts from control theory. An experimental setup, representative of a headrest of a car seat with loudspeaker-microphone distance on the order of a few centimeters, has been developed to limit the system delay. The experimental band-limited noise source has been obtained from an idling car. Our results show that the proposed system guarantees appreciable peak noise cancellation and simultaneously avoids noise amplification outside the band of interest
Experimental Results on Observation Filter Estimation for Microphone Virtualization
No full textActive Noise Control (ANC) systems exploit the superposition principle to generate a quiet acoustic zone around a confined area affected by a disturbance signal detected by a monitoring microphone. In automotive applications, the problem of noise within the car cabin has become a hot research topic. Nowadays, most of the commercial solutions generate a silence zone around the position of the monitoring microphone only. Especially for the automotive environment, to weaken disturbance signal at a different position with respect to the monitoring microphone is fundamental. The estimation of the acoustic channel between the monitoring microphone and the physical region in which the noise cancellation is targeted, referred to as observation filter, is necessary. This approach is usually known as microphone virtualization, or Virtual Microphone Technique (VMT) since the audio signal detected by the virtual microphone (e.g., targeting driver's ears) has to be retrieved starting from the monitoring ones. In this paper, a performance comparison between adaptive and fixed approaches to the estimation of the observation filter is presented. The disturbance signals are acquired in an experimental measurement campaign on a realistic car interior. Eight microphones are employed to acquire four different driving scenarios at various pace of the car. Experimental results show that, due the insufficient spectral coherence between the monitoring and virtual microphones, system performance is physically limited. A specific road and car pace scenario typically exhibits significant robustness to road mismatch. In the low frequency regime, both estimation approaches perform well. However, the fixed one guarantees improved broadband performance
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
Performance Analysis of Feedback MIMO ANC in Experimental Automotive Environment
No full textIn this paper, a performance analysis of FeedBack (FB) Active Noise Cancellation (ANC) systems for automotive applications is presented. Since the performance of FB ANC systems is strongly impaired by the delay induced by the physical distance between microphones and loudspeakers, an experimental setup representative of a car seat headrest has been developed. In this setup, the loudspeaker-microphone distance is on the order of few centimeters. An experimentally acquired band-limited noise source is obtained from an idling car. Noise reduction is performed by using a Filtered-x Least Mean Square (FxLMS) algorithm. Two 2×2 Multiple Input - Multiple Output (MIMO) schemes are considered - standard one and Filtered-Error (FE) based. Our experimental results show that the proposed MIMO systems enable improved performance and are able to control the perceived noise at two listening positions in a realistic automotive application
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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