1,721,006 research outputs found
Adaptive Interference Tolerant Receivers for Asynchronous Cooperative MIMO Communications
Full text linkAdaptive single user receivers are demonstrated in this paper for a Cooperative Virtual MIMO network applying Spread Spectrum Sequences. In asynchronous decentralized cooperative systems, it is expected that, for typical wireless environments, user transmissions from adjacent relaying nodes (and other cells) will create interference. Large scale MIMO antenna arrays can mitigate interference with sufficient degrees of freedom but they can be underdetermined in decentralized non orthogonal multiple access (NOMA). In this paper we use Spread Spectrum CDMA sequences when user cooperation and relaying is necessitated and correspondingly apply decentralized single user algorithms utilizing an adaptive multiuser detection approach. The approach does not require Channel State Information (CSI) and operates in a decentralized manner without requiring knowledge of the transmissions from other users (i.e. power, channel gain and phase, and multiuser chips). This yields a low interference cooperative MIMO communication network that is useful for communication in areas with poor coverage or to temporarily increase spectral efficiency to enable a high throughput uplink or downlink channel. The adaptive algorithm utilized in this paper is investigated for both chip-level and symbol-level optimization where it noted that when applying chip-level optimization, a more interference robust receiver can be built when utilizing processing gain (rather than receiver dimensionality) as a metric to combat interference when the number of transmitter antennas used are fixed
Relaying MIMO for cooperative mobile networks
No full textRelay networks achieve high performance by utilizing cooperation between nodes that can be classified as multi-hop networks and cooperative MIMO relaying networks. Cooperative diversity is a transmission technique to overcome fading, multipath and inter-channel interference. As an important part of “spatial diversity” systems, cooperative diversity involving multi hop data relays is a solution to improve propagation performance, expanding coverage and enhancing system capacity in such wireless environments. In a cooperative diversity system, the “third party” mobile devices acting as relays to help the main transmission link for improving the performance such as bit error rate (BER), data rate, coverage. This paper is a study of analyzing the system performance for MIMO-Relaying MIMO in different wireless channel and results show the better performance of cooperative communication
Adaptive Signal Combining with Unequal Channel Noise Variances
No full textThis paper demonstrates the signal combining by use of adaptive algorithms for wireless communication networks. The proposed adaptive combiner operates under different communication channel noise variances on each branch of the multi-antenna receiver. The used algorithm for adaptive signal combining is least mean square (LMS) algorithm based on Newton’s Recursion Method. The proposed algorithm uses inverse of noise variances estimate in step size of adaptive algorithm. It is shown that the adaptive combining filter with LMS converges with respect to signal to noise ratio (SNR) and not to the received power. Simulation results in Gaussian channels with different channel noise variances shows that proposed scheme provide performance very close to wiener’s solution of signal combining. It provide 10−4 bit error rate (BER) at 10.dB SNR. The performance of system in Flat Fading Raleigh channels is about 10−5 at 20 dB SNR. Where as the classical maximum ratio combining, adaptive combining with classical LMS and recursive least square algorithm provide 10−3 bit error rate at 20 dB SNR. The improvement in MSE and BER performance with purposed algoritm is more obvious when two independent signals arrive at the receiver of communication terminal (on multiple antennas) with 10dB of SNR difference, which is very common situation in wireless communication systems
MIMO relay channels with partial channel knowledge/estimation error and spatial correlation
No full textIn this paper we show the effect of partial channel
knowledge at the receiver which causes estimation error of the channel at the receiver and the spatial correlation on MIMO Relay wireless communication systems. We assume that the transmitter has perfect knowledge of statistical parameters of the channel such as covariance or mean. We show how the topology of the equipment can upgrade or degrade the channel and we generalize a relaying MIMO scenario. We mathematically approach the gain of a system that uses relaying antennas. We assume a Zero Mean Circular Symmetric Complex Gaussian(ZMCSCG) channel elements and ZMCSCG noise elements. As we examine spatial correlation at the transmitter only, we assume that the elements of the rows of the channel matrix of the first hop are correlated. Partial CSI at the receiver causes errors at the estimation of the channel at the receiver which results the
channel capacity to degrade and to saturate at certain levels of SNR. Numerical simulations are conducted in order to support the theoretical results used in this pape
Adaptive Signal Combining with Unequal Channel Noise Variances
No full textThis paper demonstrates the signal combining by use of adaptive algorithms for wireless communication networks. The proposed adaptive combiner operates under different communication channel noise variances on each branch of the multi-antenna receiver. The used algorithm for adaptive signal combining is least mean square (LMS) algorithm based on Newton’s Recursion Method. The proposed algorithm uses inverse of noise variances estimate in step size of adaptive algorithm. It is shown that the adaptive combining filter with LMS converges with respect to signal to noise ratio (SNR) and not to the received power. Simulation results in Gaussian channels with different channel noise variances shows that proposed scheme provide performance very close to wiener’s solution of signal combining. It provide 10−4 bit error rate (BER) at 10.dB SNR. The performance of system in Flat Fading Raleigh channels is about 10−5 at 20 dB SNR. Where as the classical maximum ratio combining, adaptive combining with classical LMS and recursive least square algorithm provide 10−3 bit error rate at 20 dB SNR. The improvement in MSE and BER performance with purposed algoritm is more obvious when two independent signals arrive at the receiver of communication terminal (on multiple antennas) with 10dB of SNR difference, which is very common situation in wireless communication systems
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
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