1,721,220 research outputs found
Performance evaluation of channel estimation techniques for MIMO-OFDM systems with adaptive sub-carrier allocation
Full text linkDynamic Sub-Carrier Allocation (DSA) strategies have been shown previously to achieve significant performance benefits when applied to OFDMA systems and further benefits for MIMOOFDMA systems. Analysis thus far has focussed on the assumption of ideal Channel State Information (CSI). In this paper, the impact of non-ideal CSI is investigated. Various channel estimation techniques are evaluated for application to MIMO-OFDMA systems. They are based on Least Squares (LS) Estimation with training pilots. ‘Conventional’ (as for MIMO-OFDM) CTP (combining training pilots and ‘improved’ (optimised for MIMO-OFDMA) STP (Separate training pilots) versions of both Frequency Domain Least Square (FDLS) and Time Domain Least Square (TDLS) channel estimation are considered, as are the options of both Space- Time Block coding (STBC) and Spatial Multiplexing (SM) as MIMO strategies. The STP-TDLS strategy is shown to significantly outperform other channel estimation options, achieving performance within 1dB of the ideal case. Subsequently, the use of the STP-TDLS channel estimation method in conjunction with the DSA algorithm is considered in order to determine the impact of non-ideal channel knowledge on the gain achieved by DSA. The performance for the cases of ideal CSI and CSI derived via STP-TDLS channel estimation are compared and evaluated for both the STBC and SM cases. The effects of non-ideal channel estimation in both the DSA mechanism and channel equalisation separately and together are evaluated. It is shown that STP-TDLS channel estimation works better in SM (only 1dB worse than ideal CSI case) than in STBC. Furthermore, it is shown that DSA is less sensitive than channel equalisation to nonideal CSI. The degradation of system performance in the realistic case of non-ideal CSI for both DSA and channel equalisation is a compound of the effects of the separate effects of non-ideal CSI error. It is shown here that in both STBC and SM cases, the effect is almost a linear addition of the two parts. Given the substantial benefits of DSA and its relative insensitivity to channel estimation errors, it is concluded that DSA remains a highly promising technique
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
Directional maximum likelihood self-estimation of the path-loss exponent
No full textThe path-loss exponent (PLE) is a key parameter in wireless propagation channels. Therefore, obtaining the knowledge of the PLE is rather significant for assisting wireless communications and networking to achieve a better performance. Most existing methods for estimating the PLE not only require nodes with known locations but also assume an omni-directional PLE. However, the location information might be unavailable or unreliable and, in practice, the PLE might change with the direction. In this paper, we are the first to introduce two directional maximum likelihood (ML) self-estimators for the PLE in wireless networks. They can individually estimate the PLE in any direction merely by locally collecting the related received signal strength (RSS) measurements. The corresponding Cramér-Rao lower bound (CRLB) is also obtained. Simulation results show that the performance of the proposed estimators is very close to the CRLB. Additionally, also for the first time, the RSSs based on only a geometric path loss are found to follow a truncated Pareto distribution in wireless random networks. This might be of great help in the analysis of wireless communications and networking.Accepted Author ManuscriptSignal Processing System
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
Overview of Spectrum Sensing for Cognitive Radio
Full text linkWe present a survey of state-of-the-art algorithms for spectrum sensing in cognitive radio. The algorithms discussed range from energy detection to sophisticated feature detectors. The feature detectors that we present all have in common that they exploit some known structure of the transmitted signal. In particular we treat detectors that exploit cyclostationarity properties of the signal, and detectors that exploit a known eigenvalue structure of the signal covariance matrix. We also consider cooperative detection. Specifically we present data fusion rules for soft and hard combining, and discuss the energy efficiency of several different sensing, sleeping and censoring schemes in detail.Accepted for publication©2010 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Erik Axell, Geert Leus and Erik G. Larsson, Overview of Spectrum Sensing for Cognitive Radio, 2010, The 2nd International Workshop on Cognitive Information Processin
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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