1,720,960 research outputs found
Delay distributions of slotted ALOHA and CSMA
No full textWe derive the closed-form delay distributions of slotted ALOHA and nonpersistent carrier sense multiple access (CSMA) protocols under steady state. Three retransmission policies are analyzed. We find that under a binary exponential backoff retransmission policy, finite average delay and finite delay variance can be guaranteed for G<2S and G<4S/3, respectively, where G is the channel traffic and S is the channel throughput. As an example, in slotted ALOHA, S<(ln2)/2 and S<3(ln4-ln3)/4 are the operating ranges for finite first and second delay moments. In addition, the blocking probability and delay performance as a function of r/sub max/ (maximum number of retransmissions allowed) is also derived
Node placement optimization in ShuffleNets
No full textNode placement problem in ShuffleNets is a combinatorial optimization problem. In this paper an efficient node placement algorithm, called the gradient algorithm, is proposed. A communication cost function between a node pair is defined and the gradient algorithm places the node pairs one by one, based on the gradient of the cost function. Then two lower bounds on the traffic weighted mean internodal distance h are proposed. The performance of the gradient algorithm is compared to the lower bounds as well as to some algorithms in the literature. Significant reduction of h̄ is obtained with the use of the gradient algorithm, especially for highly skewed traffic distributions. For a ShuffleNet with N = 64 nodes, the h̄ found is only 22% above the lower bound for the uniform random traffic distribution, and 14.7% for a highly skewed traffic distribution with skew factor γ = 100. © 1998 IEEE.link_to_subscribed_fulltex
Fixed channel assignment optimization for cellular mobile networks
No full textThe optimization of channel assignment in cellular mobile networks is an NP-complete combinatorial optimization problem. For any reasonable size network, only sub-optimal solutions can be obtained by heuristic algorithms. In this paper, six channel assignment heuristic algorithms are proposed and evaluated. They are the combinations of three channel assignment strategies and two cell ordering methods. What we found are (i) the node-color ordering of cells is a more efficient ordering method than the node-degree ordering; (ii) the frequency exhaustive strategy is more suitable for systems with highly non-uniformly distributed traffic, and the requirement exhaustive strategy is more suitable for systems with less nonuniformly distributed traffic; and (iii) the combined frequency and requirement exhaustive strategy with node-color re-ordering is the most efficient algorithm. The frequency spans obtained using the proposed algorithms are much lower than that reported in the literature, and in many cases are equal to the theoretical lower bounds.link_to_subscribed_fulltex
Performance analysis of borrowing with directional carrier locking strategy in cellular radio systems
No full textA new carrier based dynamic channel assignment for FDMA/TDMA cellular systems, called borrowing with directional carrier locking strategy, is proposed in this paper. When a call arrives at a cell and finds all voice channels busy, a carrier which consists of multiple voice channels can be borrowed from its neighboring cells for carrying the new call if such borrowing will not violate the cochannel interference constraint. Two analytical models, cell group decoupling analysis and phantom cell analysis, are constructed for evaluating the performance of the proposed strategy. Using cell group decoupling (CGD) analysis, a cell is decoupled together with its neighbors from the rest of the network for finding its call blocking probability. Unlike conventional approaches, decoupling enables the analysis to be confined to a local/small problem size and thus efficient solution can be found. For a planar cellular system with three-cell channel reuse pattern, using CGD analysis involves solving of seven-dimensional Markov chains. It becomes less efficient as the number of carriers assigned to each cell increases. To tackle this, we adopt the phantom cell analysis which can simplify the seven-dimensional Markov chain to two three-dimensional Markov chains. Using phantom cell analysis for finding the call blocking probability of a cell, two phantom cells are used to represent its six neighbors. Based on extensive numerical results, we show that the proposed strategy is very efficient in sharing resources among base stations. For low to medium traffic loads and small number of voice channels per carrier, we show that both analytical models provide accurate prediction on the system call blocking probability.link_to_subscribed_fulltex
Phantom cell analysis of dynamic channel assignment in cellular mobile systems
No full textIn this paper, we propose the phantom cell analysis for dynamic channel assignment. This is an approximate analysis that can handle realistic planar systems with the threecell channel-reuse pattern. To find the blocking probability of a particular cell, two phantom cells are used to represent its six neighboring cells. Then, by conditioning on the relative positions of the two phantom cells, the blocking probability of that particular cell can be found. We found that the phantom cell analysis is not only very accurate in predicting the blocking performance, but also very computationally efficient. Besides, it is applicable to any traffic and channel-reuse patterns. © 1998 IEEE.link_to_subscribed_fulltex
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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