1,721,215 research outputs found
Secure SWIPT for directional modulation aided AF relaying networks
No full textSecure wireless information and power transfer based on directional modulation is conceived for amplify-andforward (AF) relaying networks. Explicitly, we first formulate a secrecy rate maximization (SRM) problem, which can be decomposed into a twin-level optimization problem and solved by a one-dimensional (1D) search and semidefinite relaxation (SDR) technique. Then in order to reduce the search complexity, we formulate an optimization problem based on maximizing the signal-to-leakage-AN-noise-ratio (Max-SLANR) criterion, and transform it into a SDR problem. Additionally, the relaxation is proved to be tight according to the classic Karush-Kuhn- Tucker (KKT) conditions. Finally, to reduce the computational complexity, a successive convex approximation (SCA) scheme is proposed to find a near-optimal solution. The complexity of the SCA scheme is much lower than that of the SRM and the Max-SLANR schemes. Simulation results demonstrate that the performance of the SCA scheme is very close to that of the SRM scheme in terms of its secrecy rate and bit error rate (BER), but much better than that of the zero forcing (ZF) scheme.</p
IRS-aided wireless powered MEC systems: TDMA or NOMA for computation offloading?
No full textAn intelligent reflecting surface (IRS)-aided wirelesspowered
mobile edge computing (WP-MEC) system is conceived, where each device’s
computational task can be divided into two parts for local computing and
offloading to mobile edge computing (MEC) servers, respectively. Both time
division multiple access (TDMA) and non-orthogonal multiple access (NOMA)
schemes are considered for uplink (UL) offloading. To fully unleash the
potential benefits of the IRS, employing multiple IRS beamforming (BF)
patterns/vectors in the considered operating frame
to create timeselectivity channels, i.e., dynamic IRS BF (DIBF), is in
principle possible at the cost of additional signaling overhead. To strike a
balance between the system performance and associated signalling overhead, we
propose three cases of DIBF configurations based on the maximum number of IRS
reconfiguration times. The degree-of-freedom provided by the IRS may introduce
different impacts on the TDMA and NOMA-based UL offloading schemes. Thus, it is
still fundamentally unknown which multiple access scheme is
superior for MEC UL offloading by considering the
impact of the IRS. To answer this question, we provide a comprehensively
theoretical performance comparison for the TDMA and NOMA-based offloading
schemes under the three cases of DIBF configurations by characterizing their
achievable computation rate. Analytical results demonstrate that offloading
adopting TDMA can achieve the same computation rate as that of NOMA, when all
the devices share the same IRS BF vector during the UL offloading. By contrast,
computation offloading exploiting TDMA outperforms NOMA, when the IRS BF vector
can be flexibly adapted for UL offloading. Then, we propose computationally
efficient algorithms by invoking alternating optimization for solving their
associated computation rate maximization problems. Our numerical results
demonstrate the significant performance gains
achieved by the proposed designs over various benchmark schemes and also unveil
that the optimal time allocated to downlink wireless power transfer can be
effectively reduced with the aid of IRSs, which is beneficial for both the
system’s spectral efficiency and its energy efficiency.</p
Cooperative multi-satellite and multi-RIS beamforming: Enhancing LEO SatCom and mitigating LEO-GEO intersystem interference
No full text
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
Secure UAV-to-ground MIMO communications: Joint transceiver and location optimization
No full textUnmanned aerial vehicles (UAVs) are foreseen to constitute promising airborne communication devices as a benefit of their superior channel quality. But UAV-to-ground (U2G) communications are vulnerable to eavesdropping. Hence, we conceive a sophisticated physical layer security solution for improving the secrecy rate of multi-antenna aided U2G systems. Explicitly, the secrecy rate of the U2G MIMO wiretap channels is derived by using random matrix theory. The resultant explicit expression is then applied in the joint optimization of the MIMO transceiver and the UAV location relying on an alternating optimization technique. Our numerical results show that thejoint transceiver and location optimization conceived facilitates secure communications even in the challenging scenario, where the legitimate channel of confidential information is inferior to the eavesdropping channel
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