On the ergodic sum-rate performance of CDD in multi-user systems

The main focus of space-time coding design and analysis for MIMO systems has been so far focused on single-user systems. For single-user systems, transmit diversity schemes suffer a loss in spectral efficiency if the receiver is equipped with more than one antenna, making them unsuitable for high rate transmission. One such transmit diversity scheme is the cyclic delay diversity code (CDD). The advantage of CDD over other diversity schemes such as orthogonal space-time block codes (OSTBC) is that a code rate of one and delay optimality are achieved independent of the number of transmit antennas. In this work we analyze the ergodic rate of a multi-user multiple access channel (MAC) with each user applying such a cyclic delay diversity (CDD) code. We derive closed form expressions for the ergodic sum-rate of multi-user CDD and compare it with the sum-capacity. We study the ergodic rate region and show that in contrast to what is conventionally known regarding the single-user case, transmit diversity schemes are viable candidates for high rate transmission in multi-user systems. Finally, our theoretical findings are illustrated by numerical simulation results.Comment: to appear in Proceedings of 2007 IEEE Information Theory Workshop (ITW) in Lake Taho

Financiación de la educación superior en los países árabes. Problemas y desafíos

Este artículo muestra que el 75% de las universidades de los países árabes han surgido en las últimas dos décadas del siglo XX. Los fondos destinados a la financiación de la educación superior varían mucho según los países. En algunos el gasto total per cápita en educación privada es de 100 USD o más (como en Kuwait, Arabia Saudí o Qatar), y en otros no llega a los 10 USD (como en Sudán, Yemen o Mauritania). En los últimos nueve años hemos presenciado una reducción importante de los recursos destinados a la educación superior en los países árabes.Peer Reviewe

Achievable and Crystallized Rate Regions of the Interference Channel with Interference as Noise

The interference channel achievable rate region is presented when the interference is treated as noise. The formulation starts with the 2-user channel, and then extends the results to the n-user case. The rate region is found to be the convex hull of the union of n power control rate regions, where each power control rate region is upperbounded by a (n-1)-dimensional hyper-surface characterized by having one of the transmitters transmitting at full power. The convex hull operation lends itself to a time-sharing operation depending on the convexity behavior of those hyper-surfaces. In order to know when to use time-sharing rather than power control, the paper studies the hyper-surfaces convexity behavior in details for the 2-user channel with specific results pertaining to the symmetric channel. It is observed that most of the achievable rate region can be covered by using simple On/Off binary power control in conjunction with time-sharing. The binary power control creates several corner points in the n-dimensional space. The crystallized rate region, named after its resulting crystal shape, is hence presented as the time-sharing convex hull imposed onto those corner points; thereby offering a viable new perspective of looking at the achievable rate region of the interference channel.Comment: 28 pages, 12 figures, to appear in IEEE Transactions of Wireless Communicatio

Runtime Enforcement for Component-Based Systems

Runtime enforcement is an increasingly popular and effective dynamic validation technique aiming to ensure the correct runtime behavior (w.r.t. a formal specification) of systems using a so-called enforcement monitor. In this paper we introduce runtime enforcement of specifications on component-based systems (CBS) modeled in the BIP (Behavior, Interaction and Priority) framework. BIP is a powerful and expressive component-based framework for formal construction of heterogeneous systems. However, because of BIP expressiveness, it remains difficult to enforce at design-time complex behavioral properties. First we propose a theoretical runtime enforcement framework for CBS where we delineate a hierarchy of sets of enforceable properties (i.e., properties that can be enforced) according to the number of observational steps a system is allowed to deviate from the property (i.e., the notion of k-step enforceability). To ensure the observational equivalence between the correct executions of the initial system and the monitored system, we show that i) only stutter-invariant properties should be enforced on CBS with our monitors, ii) safety properties are 1-step enforceable. Given an abstract enforcement monitor (as a finite-state machine) for some 1-step enforceable specification, we formally instrument (at relevant locations) a given BIP system to integrate the monitor. At runtime, the monitor observes and automatically avoids any error in the behavior of the system w.r.t. the specification. Our approach is fully implemented in an available tool that we used to i) avoid deadlock occurrences on a dining philosophers benchmark, and ii) ensure the correct placement of robots on a map.Comment: arXiv admin note: text overlap with arXiv:1109.5505 by other author

Gender and educational differences in the association between smoking and health-related quality of life in Belgium

Previous studies have shown that smoking has a significant and negative association with health-related quality of life (HRQOL). A question remains, however, as to whether this association between smoking and HRQOL differs by gender or educational level. To examine this question, we extracted data from the 2013 Belgian Health Interview Survey (n = 5668). HRQOL was assessed using the descriptive system of the EuroQol 5D-5L that consists of 5 dimensions and the resulting index score. Linear and logistic multivariable regression models were fitted to estimate the association between HRQOL and smoking for each educational level and gender. Also, interaction terms were introduced in the full regression models and the Wald test was used to assess model fit. Our findings show that among men, there is no significant association between smoking and HRQOL, and no effect modification by educational level. Among women, however, daily smokers have shown significantly lower HRQOL scores compared with never smokers, but only among females with a low and intermediate educational level. The lower EQ-5D index scores among female daily smokers with lower education was due to higher odds of reporting problems in anxiety/depression, mobility, pain, and usual activities. To conclude, information on the association between HRQOL and smoking is useful for the development of smoking cessation interventions. Our findings suggest the importance of tailoring these interventions to the needs of the women with lower education

Survie Digitale : Les Entreprises à l'Épreuve de la Numérisation et de la Durabilité

This study delves into the profound implications of digitization on corporate sustainability, highlighting its crucial role in the potential prevention of failure. A methodical approach has been adopted, involving careful analysis of a variety of scientific sources. Extensive research from reputable scientific sources and empirical evidence have been rigorously examined to clearly elucidate the complex links between digitization, sustainability, and corporate failure prevention. Concrete examples vividly illustrate the principles outlined. In addition, fine-tuned resolutions and exemplary methods are suggested for mitigating the risks of potential failure, highlighting notable business success stories. The underlying methodology relies on a thorough review of academic literature, the collection of empirical data and a logical structure to present the links between digitization, sustainability, and business failure. Anticipated results include an in-depth understanding of these interactions, with proposals for relevant resolutions. This composition offers an informed, structured, and persuasive perspective on this crucial intersection, prompting future explorations in yet unexplored areas of research.Cette étude plonge dans les implications profondes de la numérisation sur la pérennité des entreprises, en mettant en évidence son rôle crucial dans la prévention potentielle de la défaillance. Une approche méthodique a été adoptée, impliquant une analyse minutieuse de diverses sources scientifiques. Des recherches approfondies provenant de sources scientifiques réputées et des preuves empiriques ont été rigoureusement examinées pour clairement élucider les liens complexes entre la numérisation, la durabilité et la prévention des défaillances des entreprises. Des exemples concrets illustrent vivement les principes exposés. De plus, des résolutions fines et des méthodes exemplaires sont suggérées pour atténuer les risques de défaillance potentielle, mettant en lumière les réussites notables dans le domaine des affaires. La méthodologie sous-jacente repose sur une revue approfondie de la littérature académique, la collecte de données empiriques et une structure logique pour présenter les liens entre la numérisation, la durabilité et la défaillance des entreprises. Les résultats anticipés incluent une compréhension approfondie de ces interactions, avec des propositions de résolutions pertinentes. Cette composition offre une perspective éclairée, structurée et persuasive sur cette intersection cruciale, incitant à des explorations futures dans des domaines de recherche encore inexplorés