We develop a novel design framework for energy-efficient spectrum sharing among autonomous users who aim to minimize their energy consumptions subject to minimum throughput requirements. Most existing works proposed stationary spectrum sharing policies, in which users transmit at fixed power levels. Since users transmit simultaneously under stationary policies, to fulfill minimum throughput requirements, they need to transmit at high power levels to overcome interference. To improve energy efficiency, we construct nonstationary spectrum sharing policies, in which the users transmit at time-varying power levels. Specifically, we focus on TDMA (time-division multiple access) policies in which one user transmits at each time (but not in a round-robin fashion). The proposed policy can be implemented by each user running a low-complexity algorithm in a decentralized manner. It achieves high energy efficiency even when the users have erroneous and binary feedback about their interference levels. Moreover, it can adapt to the dynamic entry and exit of users. The proposed policy is also deviation-proof, namely autonomous users will find it in their self-interests to follow it. Compared to existing policies, the proposed policy can achieve an energy saving of up to 90 when the number of users is high.
In this section, we provide a comprehensive comparison between the proposed scheme and existing works. The reader could skip this section and go directly to the system model, if not interested in the detailed comparisons. Although only some works @cite_23 -- @cite_10 use the same problem formulation as ours, we compare against a wide range of related works @cite_4 -- @cite_12 to highlight the technical novelty of our work, and to illustrate that the works @cite_4 -- @cite_7 @cite_21 -- @cite_12 proposed under different problem formulations cannot be adapted to our setting.
@cite_4 @cite_7 @cite_21 @cite_23 @cite_10 @cite_12
2520925521 2021672791 625673688 2971432649
We propose a novel approach based on Formal Concept Analysis for Topic Detection.Our proposal overcomes traditional problems of the clustering and classification techniques.We analyse the parameters involved in the process in a Twitter-based framework.We propose a topic selection methodology based on the stability concept.We overcome the state-of-the-art results for the task. The Topic Detection Task in Twitter represents an indispensable step in the analysis of text corpora and their later application in Online Reputation Management. Classification, clustering and probabilistic techniques have been traditionally applied, but they have some well-known drawbacks such as the need to fix the number of topics to be detected or the problem of how to integrate the prior knowledge of topics with the detection of new ones. This motivates the current work, where we present a novel approach based on Formal Concept Analysis (FCA), a fully unsupervised methodology to group similar content together in thematically-based topics (i.e., the FCA formal concepts) and to organize them in the form of a concept lattice. Formal concepts are conceptual representations based on the relationships between tweet terms and the tweets that have given rise to them. It allows, in contrast to other approaches in the literature, their clear interpretability. In addition, the concept lattice represents a formalism that describes the data, explores correlations, similarities, anomalies and inconsistencies better than other representations such as clustering models or graph-based representations. Our rationale is that these theoretical advantages may improve the Topic Detection process, making them able to tackle the problems related to the task. To prove this point, our FCA-based proposal is evaluated in the context of a real-life Topic Detection task provided by the Replab 2013 CLEF Campaign. To demonstrate the efficiency of the proposal, we have carried out several experiments focused on testing: (a) the impact of terminology selection as an input to our algorithm, (b) the impact of concept selection as the outcome of our algorithm, and; (c) the efficiency of the proposal to detect new and previously unseen topics (i.e., topic adaptation). An extensive analysis of the results has been carried out, proving the suitability of our proposal to integrate previous knowledge of prior topics without losing the ability to detect novel and unseen topics as well as improving the best Replab 2013 results. Software engineers often use high-level models (for instance, box and arrow sketches) to reason and communicate about an existing software system. One problem with high-level models is that they are almost always inaccurate with respect to the system's source code. We have developed an approach that helps an engineer use a high-level model of the structure of an existing software system as a lens through which to see a model of that system's source code. In particular, an engineer de nes a high-level model and speci es how the model maps to the source. A tool then computes a software re exion model that shows where the engineer's high-level model agrees with and where it di ers from a model of the source. The paper provides a formal characterization of reexion models, discusses practical aspects of the approach, and relates experiences of applying the approach and tools to a number of di erent systems. The illustrative example used in the paper describes the application of re exion models to NetBSD, an implementation of Unix comprised of 250,000 lines of C code. In only a few hours, an engineer computed several re exion models that provided him with a useful, global overview of the structure of the NetBSD virtual memory subsystem. The approach has also been applied to aid in the understanding and experimental reengineering of the Microsoft Excel spreadsheet product. This research was funded in part by the NSF grant CCR-8858804 and a Canadian NSERC post-graduate scholarship. 0 Permission to make digital hard copies of all or part of this material without fee is granted provided that the copies are not made or distributed for pro t or commercial advantage, the ACM copyright server notice, the title of the publication and its date appear, and notice is given that copyright is by permission of the Association for Computing Machinery, Inc. (ACM). To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior speci c permission and or a fee. SIGSOFT '95 Washington, D.C., USA c 1995 ACM 0-89791-716-2 95 0010...$3.50 Les recherches presentees dans cette these portent sur la modelisation et la resolution de systemes de contraintes, en considerant aussi bien l'aspect theorique que l'aspect pratique. La partie theorique a comme objectif de proposer des methodes generiques qui exploitent des techniques de la Programmation Par Contraintes et de la Programmation Mathematique pour modeliser et resoudre des systemes de contraintes binaires. Nous avons propose une formulation lineaire agregee pour les CSP binaires et une methode de filtrage combinant la relaxation Lagrangienne et la consistance d'arc. Pour les CSP sur-contraints, nous avons introduit la notion d'inegalite binaire valide. Nous avons egalement montre comment exploiter cette notion pour ameliorer les bornes inferieures qui se basent sur la consistance d'arc et proposer de nouvelles bornes inferieures ainsi qu'une technique de pretraitement de WCSP. Dans la partie appliquee, nous avons traite le probleme de placement des arrets et de la production des reacteurs nuclaires d'Electricite de Fance(EDF). Nous avons ameliore la modelisation mathematique actuelle de certaines contraintes du probleme et nous avons propose une nouvelle modelisation en Programmation Par Contraintes pour tout le probleme. Nous avons, par la suite, concu le solveur OSOPAN pour la satisfaction et l'optimisation de ce probleme. Ce solveur fait cooperer la Programmation Par Contraintes, la Programmation Mathematique ainsi que la Recherche Locale. Abstract In this paper, we present a unifying analysis for redundancy systems with cancel-on-start ( c . o . s . ) and cancel-on-complete ( c . o . c . ) with exponentially distributed service requirements. With c . o . s . ( c . o . c . ) all redundant copies are removed as soon as one of the copies starts (completes) service. As a consequence, c . o . s . does not waste any computing resources, as opposed to c . o . c . We show that the c . o . s . model is equivalent to a queueing system with multi-type jobs and servers, which was analyzed in , (2012), and show that c . o . c . (under the assumption of i.i.d. copies) can be analyzed by a generalization of , (2012) where state-dependent departure rates are permitted. This allows us to show that the stationary distribution for both the c . o . c . and c . o . s . models has a product form. We give a detailed first-time analysis for c . o . s and derive a closed form expression for important metrics like mean number of jobs in the system, and probability of waiting. We also note that the c . o . s . model is equivalent to Join-Shortest-Work queue with power of d (JSW( d )). In the latter, an incoming job is dispatched to the server with smallest workload among d randomly chosen ones. Thus, all our results apply mutatis-mutandis to JSW( d ). Comparing the performance of c . o . s . with that of c . o . c . with i.i.d. copies gives the unexpected conclusion (since c . o . s . does not waste any resources) that c . o . s . is worse in terms of mean number of jobs. As part of ancillary results, we illustrate that this is primarily due to the assumption of i.i.d. copies in case of c . o . c . (together with exponentially distributed requirements) and that such assumptions might lead to conclusions that are qualitatively different from that observed in practice.