1,720,978 research outputs found
MMSE Receiver Design and SINR Calculation in MU-MIMO Systems with Imperfect CSI
Full text linkThe performance of the uplink of multiuser multiple input multiple output systems depends critically on the receiver architecture and on the quality of the acquired channel state information. A popular approach is to design linear receivers that minimize the mean squared error (MSE) of the received data symbols. Unfortunately, most of the literature does not take into account the presence of channel state information errors in the MSE minimization. In this letter we develop a linear minimum MSE (MMSE) receiver that employs the noisy instantaneous channel estimates to minimize the MSE, and highlight the dependence of the receiver performance on the pilot-to-data power ratio. By invoking the theory of random matrices, we calculate the users’ signal-to-interference-plus-noise ratio as a function of the number of antennas and the pilot-to-data power ratio of all users. Numerical results indicate that this new linear receiver outperforms the classical mismatched MMSE receiver
Modelling large timescale and small timescale service variability
Full text linkThe performance of service units might depend on various randomly changing environmental effects. It is quite often the case that these effects varies on different time scales. In this paper we consider short and long scale service variability, where the short scale variability affects the instantaneous service speed of the service unit and the large scale effect is defined by a modulating background Markov chain. The main modelling challenge is that the considered short and long range variation results randomness along different axes, the short scale variability along the time axis and the long scale variability along the work axis. The work presents mostly simulation results; the mathematical setup for analytical results is provided, but the actual analysis is subject to future research
Experimental analysis of the correlation of HTTP GET invocations
No full textIn this paper we experimentally investigate if optimal retry times can be determined based on models that assume independence of successive tries. We do this using data obtained for HTTP GET. This data provides application-perceived timing characteristics for the various phases of web page download, including response times for TCP connection set-ups and individual object downloads. The data consists of pairs of consecutive downloads for over one thousand randomly chosen URLs. Our analysis shows that correlation exists for normally completed invocations, but is remarkably low for relatively slow downloads. This implies that for typical situations in which retries are applied, models relying on the independence assumption are appropriate
Mixed finite-/infinite-capacity priority queue with interclass correlation
No full textWe consider a discrete-time queueing system with two priority classes and absolute priority scheduling. In our model, we capture potential correlation between the arrivals of the two priority classes. For practical use, it is required that the high-priority queue is of (relatively) small size and we hence use a model with finite high-priority queue capacity. We obtain expressions for the probability mass functions of the steady-state system content and delay of the high-priority class as well as for the probability generating functions and moments of the steady-state system content and delay of the low-priority class. The results are compared to those of a similar system, but with an infinite capacity for high priority packets, and it is shown that the latter can be inaccurate. We also investigate the effect of correlation between the arrivals of both priority classes on the performance of the system
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 a Linear MMSE Receiver in Time-Variant Rayleigh Fading Channels
No full textThe performance of the uplink of single and multiuser multiple input multiple output (MIMO) systems depends crucially on the receiver architecture and the quality of channel state information at the receiver. Therefore, several previous works have developed minimum mean squared error (MMSE) receivers and proposed balancing the resources spent on acquiring channel state information and transmitting the payload of data packets. Somewhat surprisingly, the most popular MIMO linear MMSE receivers do not exploit the correlation structure that is present in autoregressive Rayleigh fading environments. Therefore, in this article we first develop a new linear receiver that not only takes channel state information errors into account in minimizing the MSE of the received data symbols, but it also utilizes that the subsequent noisy channel coefficients are correlated. For this new linear MMSE receiver, we derive the achieved MSE as a function of the number of receive antennas and the pilot-to-data power ratio. Interestingly, we find that the pilot power that minimizes the MSE of the data symbols does not depend on the number of antennas and that the new linear MMSE receiver outperforms previously proposed MIMO receivers when the autocorrelation coefficient of the channel is high.</p
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